sslctx.hpp

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//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012- OpenVPN Inc.
//
//    SPDX-License-Identifier: MPL-2.0 OR AGPL-3.0-only WITH openvpn3-openssl-exception
//
 
// Wrap the OpenSSL SSL API as defined in <openssl/ssl.h>
// so that it can be used as the SSL layer by the OpenVPN core.
 
#ifndef OPENVPN_OPENSSL_SSL_SSLCTX_H
#define OPENVPN_OPENSSL_SSL_SSLCTX_H
 
#include <map>
#include <mutex>
#include <string>
#include <cstring>
#include <cstdint>
#include <sstream>
#include <utility>
 
#include <openssl/crypto.h>
#include <openssl/ssl.h>
#include <openssl/x509v3.h>
#include <openssl/rsa.h>
#include <openssl/dsa.h>
#include <openssl/ec.h>
#include <openssl/bn.h>
#include <openssl/rand.h>
#include <openssl/evp.h>
#include <openssl/opensslv.h>
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
#include <openssl/provider.h>
#endif
 
#include <openvpn/common/size.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/common/mode.hpp>
#include <openvpn/common/options.hpp>
#include <openvpn/common/base64.hpp>
#include <openvpn/common/string.hpp>
#include <openvpn/common/uniqueptr.hpp>
#include <openvpn/common/hexstr.hpp>
#include <openvpn/common/numeric_cast.hpp>
#include <openvpn/common/to_string.hpp>
#include <openvpn/common/unicode.hpp>
#include <openvpn/frame/frame.hpp>
#include <openvpn/buffer/buffer.hpp>
#include <openvpn/pki/cclist.hpp>
#include <openvpn/pki/epkibase.hpp>
#include <openvpn/ssl/kuparse.hpp>
#include <openvpn/ssl/nscert.hpp>
#include <openvpn/ssl/tlsver.hpp>
#include <openvpn/ssl/tls_remote.hpp>
#include <openvpn/ssl/verify_x509_name.hpp>
#include <openvpn/ssl/peer_fingerprint.hpp>
#include <openvpn/ssl/sslconsts.hpp>
#include <openvpn/ssl/sslapi.hpp>
#include <openvpn/ssl/sni_handler.hpp>
#include <openvpn/ssl/iana_ciphers.hpp>
#include <openvpn/openssl/util/error.hpp>
#if ENABLE_EXTERNAL_PKI
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
#include <openvpn/openssl/pki/xkey.hpp>
#else
#include <openvpn/openssl/pki/extpki.hpp>
#endif
#endif
#include <openvpn/openssl/pki/x509.hpp>
#include <openvpn/openssl/pki/crl.hpp>
#include <openvpn/openssl/pki/pkey.hpp>
#include <openvpn/openssl/pki/dh.hpp>
#include <openvpn/openssl/pki/x509store.hpp>
#include <openvpn/openssl/pki/x509certinfo.hpp>
#include <openvpn/openssl/bio/bio_memq_stream.hpp>
#include <openvpn/openssl/ssl/sess_cache.hpp>
#include <openvpn/openssl/ssl/tlsver.hpp>
 
 
#ifdef HAVE_JSON
#include <openvpn/common/jsonhelper.hpp>
#endif
 
// An SSL Context is essentially a configuration that can be used
// to generate an arbitrary number of actual SSL connections objects.
 
// OpenSSLContext is an SSL Context implementation that uses the
// OpenSSL library as a backend.
 
#if OPENSSL_VERSION_NUMBER < 0x30000000L
using ssl_mac_ctx = ::HMAC_CTX;
#else
using ssl_mac_ctx = ::EVP_MAC_CTX;
#endif
 
namespace openvpn {
 
// Represents an SSL configuration that can be used
// to instantiate actual SSL sessions.
class OpenSSLContext : public SSLFactoryAPI
{
    using SSL_CTX_unique_ptr = std::unique_ptr<::SSL_CTX, decltype(&::SSL_CTX_free)>;
 
  public:
    using Ptr = RCPtr<OpenSSLContext>;
    using CertCRLList = CertCRLListTemplate<OpenSSLPKI::X509List, OpenSSLPKI::CRLList>;
 
    enum
    {
        MAX_CIPHERTEXT_IN = 64 // maximum number of queued input ciphertext packets
    };
 
    class Config : public SSLConfigAPI
    {
        friend class OpenSSLContext;
 
        // These can be OR-ed to provide different OpenSSL library configurations.
        static constexpr unsigned short LIB_CTX_NO_PROVIDERS = 0;
        static constexpr unsigned short LIB_CTX_LEGACY_PROVIDER = (1 << 0);
 
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
        /* OpenSSL library context, used to load non-default providers etc,
         * made mutable so const function can use/initialise the context.
         *
         * First field in this class so it gets destructed last*/
        using TlsLibCtxType = std::remove_pointer<SSLLib::Ctx>::type;
        using TlsLibCtxUPtr = std::unique_ptr<TlsLibCtxType, decltype(&::OSSL_LIB_CTX_free)>;
        using SSLProviderUPtr = std::unique_ptr<OSSL_PROVIDER, decltype(&::OSSL_PROVIDER_unload)>;
 
        class LibContext
        {
          public:
            LibContext(unsigned short config)
                : ctx_{OSSL_LIB_CTX_new(), &::OSSL_LIB_CTX_free}
            {
                if (!ctx_)
                    throw OpenSSLException("OpenSSLContext: OSSL_LIB_CTX_new failed");
 
                if (config & LIB_CTX_LEGACY_PROVIDER)
                {
                    SSLProviderUPtr legacy_provider{OSSL_PROVIDER_load(ctx_.get(), "legacy"), &::OSSL_PROVIDER_unload};
 
                    if (!legacy_provider)
                        throw OpenSSLException("OpenSSLContext: loading legacy provider failed");
 
                    SSLProviderUPtr default_provider{OSSL_PROVIDER_load(ctx_.get(), "default"), &::OSSL_PROVIDER_unload};
 
                    if (!default_provider)
                        throw OpenSSLException("OpenSSLContext: loading default provider failed");
 
                    providers_.emplace_back(std::move(legacy_provider));
                    providers_.emplace_back(std::move(default_provider));
                }
            }
 
            SSLLib::Ctx ctx() const
            {
                return ctx_.get();
            }
 
          private:
            TlsLibCtxUPtr ctx_;
            std::vector<SSLProviderUPtr> providers_;
        };
#endif
 
      public:
        using Ptr = RCPtr<Config>;
 
        SSLFactoryAPI::Ptr new_factory() override
        {
            return SSLFactoryAPI::Ptr(new OpenSSLContext(this));
        }
 
        void set_mode(const Mode &mode_arg) override
        {
            mode = mode_arg;
        }
 
        const Mode &get_mode() const override
        {
            return mode;
        }
 
        // if this callback is defined, no private key needs to be loaded
        void set_external_pki_callback(ExternalPKIBase *external_pki_arg, const std::string &alias) override
        {
            external_pki = external_pki_arg;
            external_pki_alias = alias;
        }
 
        // server side
        void set_session_ticket_handler(TLSSessionTicketBase *session_ticket_handler_arg) override
        {
            session_ticket_handler = session_ticket_handler_arg;
        }
 
        // client side
        void set_client_session_tickets(const bool v) override
        {
            client_session_tickets = v;
        }
 
        void enable_legacy_algorithms(const bool v) override
        {
            if (v)
                lib_ctx_provider_config |= LIB_CTX_LEGACY_PROVIDER;
            else
                lib_ctx_provider_config &= ~LIB_CTX_LEGACY_PROVIDER;
        }
 
        // server side
        void set_sni_handler(SNI::HandlerBase *sni_handler_arg) override
        {
            sni_handler = sni_handler_arg;
        }
 
        // client side
        void set_sni_name(const std::string &sni_name_arg) override
        {
            sni_name = sni_name_arg;
        }
 
        void set_cn_reject_handler(CommonNameReject *cn_reject_handler_arg) override
        {
            cn_reject_handler = cn_reject_handler_arg;
        }
 
        void set_private_key_password(const std::string &pwd) override
        {
            pkey.set_private_key_password(pwd);
        }
 
        void load_ca(const std::string &ca_txt, bool strict) override
        {
            ca.parse_pem(ca_txt, "ca");
        }
 
        void load_crl(const std::string &crl_txt) override
        {
            ca.parse_pem(crl_txt, "crl");
        }
 
        void load_cert(const std::string &cert_txt) override
        {
            cert.parse_pem(cert_txt, "cert");
        }
 
        void load_cert(const std::string &cert_txt, const std::string &extra_certs_txt) override
        {
            load_cert(cert_txt);
            if (!extra_certs_txt.empty())
                CertCRLList::from_string(extra_certs_txt, "extra-certs", &extra_certs, nullptr);
        }
 
        void load_private_key(const std::string &key_txt) override
        {
            pkey.parse_pem(key_txt, "private key", ctx());
        }
 
        void load_dh(const std::string &dh_txt) override
        {
            dh.parse_pem(dh_txt);
        }
 
        std::string extract_ca() const override
        {
            return ca.certs.render_pem();
        }
 
        std::string extract_crl() const override
        {
            return ca.crls.render_pem();
        }
 
        std::string extract_cert() const override
        {
            return cert.render_pem();
        }
 
        std::vector<std::string> extract_extra_certs() const override
        {
            std::vector<std::string> ret;
 
            for (const auto &cert : extra_certs)
                ret.push_back(cert.render_pem());
 
            return ret;
        }
 
        std::string extract_private_key() const override
        {
            return pkey.render_pem();
        }
 
        std::string extract_dh() const override
        {
            return dh.render_pem();
        }
 
        PKType::Type private_key_type() const override
        {
            if (!pkey.defined())
                return PKType::PK_NONE;
            return pkey.key_type();
        }
 
        size_t private_key_length() const override
        {
            return pkey.key_length();
        }
 
        void set_frame(const Frame::Ptr &frame_arg) override
        {
            frame = frame_arg;
        }
 
        void set_debug_level(const int debug_level) override
        {
            set_log_level(debug_level);
        }
 
        void set_flags(const unsigned int flags_arg) override
        {
            flags = flags_arg;
        }
 
        void set_ns_cert_type(const NSCert::Type ns_cert_type_arg) override
        {
            ns_cert_type = ns_cert_type_arg;
        }
 
        void set_remote_cert_tls(const KUParse::TLSWebType wt) override
        {
            KUParse::remote_cert_tls(wt, ku, eku);
        }
 
        void set_tls_remote(const std::string &tls_remote_arg) override
        {
            tls_remote = tls_remote_arg;
        }
 
        void set_tls_version_min(const TLSVersion::Type tvm) override
        {
            tls_version_min = tvm;
        }
 
        void set_tls_version_max(const TLSVersion::Type tvm) override
        {
            tls_version_max = tvm;
        }
 
        void set_tls_version_min_override(const std::string &override) override
        {
            TLSVersion::apply_override(tls_version_min, override);
        }
 
        void set_tls_cert_profile(const TLSCertProfile::Type type) override
        {
            tls_cert_profile = type;
        }
 
        void set_tls_cert_profile_override(const std::string &override) override
        {
            TLSCertProfile::apply_override(tls_cert_profile, override);
        }
 
        virtual void set_tls_cipher_list(const std::string &override)
        {
            if (!override.empty())
                tls_cipher_list = override;
        }
 
        virtual void set_tls_ciphersuite_list(const std::string &override)
        {
            if (!override.empty())
                tls_ciphersuite_list = override;
        }
 
        virtual void set_tls_groups(const std::string &groups)
        {
            if (!groups.empty())
                tls_groups = groups;
        }
 
        void set_local_cert_enabled(const bool v) override
        {
            local_cert_enabled = v;
        }
 
        void set_x509_track(X509Track::ConfigSet x509_track_config_arg) override
        {
            x509_track_config = std::move(x509_track_config_arg);
        }
 
        void set_rng(const StrongRandomAPI::Ptr &rng_arg) override
        {
            // Not implemented because OpenSSL is hardcoded to use its own RNG.
        }
 
        std::string validate_cert(const std::string &cert_txt) const override
        {
            OpenSSLPKI::X509 cert(cert_txt, "cert");
            return cert.render_pem();
        }
 
        std::string validate_cert_list(const std::string &certs_txt) const override
        {
            CertCRLList certs(certs_txt, "cert list");
            return certs.render_pem();
        }
 
        std::string validate_private_key(const std::string &key_txt) const override
        {
            OpenSSLPKI::PKey pkey(key_txt, "private key", ctx());
            return pkey.render_pem();
        }
 
        std::string validate_dh(const std::string &dh_txt) const override
        {
            OpenSSLPKI::DH dh(dh_txt);
            return dh.render_pem();
        }
 
        std::string validate_crl(const std::string &crl_txt) const override
        {
            OpenSSLPKI::CRL crl(crl_txt);
            return crl.render_pem();
        }
 
        void load(const OptionList &opt, const unsigned int lflags) override
        {
            // client/server
            if (lflags & LF_PARSE_MODE)
                mode = opt.exists("client") ? Mode(Mode::CLIENT) : Mode(Mode::SERVER);
 
            // possibly disable peer cert verification
            if ((lflags & LF_ALLOW_CLIENT_CERT_NOT_REQUIRED)
                && opt.exists("client-cert-not-required"))
                flags |= SSLConst::NO_VERIFY_PEER;
 
            // sni
            {
                const std::string name = opt.get_optional("sni", 1, 256);
                if (!name.empty())
                    set_sni_name(name);
            }
 
            // ca
            {
                std::string ca_txt = opt.cat("ca");
                if (lflags & LF_RELAY_MODE)
                    ca_txt += opt.cat("relay-extra-ca");
                load_ca(ca_txt, true);
            }
 
            // CRL
            {
                const std::string crl_txt = opt.cat("crl-verify");
                if (!crl_txt.empty())
                    load_crl(crl_txt);
            }
 
            // local cert/key
            if (local_cert_enabled)
            {
                // cert
                {
                    const std::string &cert_txt = opt.get("cert", 1, Option::MULTILINE);
                    const std::string ec_txt = opt.cat("extra-certs");
                    load_cert(cert_txt, ec_txt);
                }
 
                // private key
                if (!external_pki)
                {
                    const std::string &key_txt = opt.get("key", 1, Option::MULTILINE);
                    load_private_key(key_txt);
                }
            }
 
            // DH
            if (mode.is_server() && opt.exists("dh"))
            {
                const std::string &dh_txt = opt.get("dh", 1, Option::MULTILINE);
                load_dh(dh_txt);
            }
 
            // relay mode
            std::string relay_prefix;
            if (lflags & LF_RELAY_MODE)
                relay_prefix = "relay-";
 
            // ns-cert-type
            ns_cert_type = NSCert::ns_cert_type(opt, relay_prefix);
 
            // parse remote-cert-x options
            KUParse::remote_cert_tls(opt, relay_prefix, ku, eku);
            KUParse::remote_cert_ku(opt, relay_prefix, ku);
            KUParse::remote_cert_eku(opt, relay_prefix, eku);
 
            // parse tls-remote
            tls_remote = opt.get_optional(relay_prefix + "tls-remote", 1, 256);
 
            // parse verify-x509-name
            verify_x509_name.init(opt, relay_prefix);
 
            // parse peer-fingerprint
            peer_fingerprints = PeerFingerprints(opt, OpenSSLPKI::x509_fingerprint_size());
            if (peer_fingerprints)
                flags |= SSLConst::VERIFY_PEER_FINGERPRINT; // make CA optional
 
            // Parse tls-version-min option.
            tls_version_min = TLSVersion::parse_tls_version_min(opt, relay_prefix, maxver());
 
            // parse tls-cert-profile
            tls_cert_profile = TLSCertProfile::parse_tls_cert_profile(opt, relay_prefix);
 
            // Overrides for tls cipher suites
            if (opt.exists("tls-cipher"))
                tls_cipher_list = opt.get_optional("tls-cipher", 1, 256);
 
            if (opt.exists("tls-ciphersuites"))
                tls_ciphersuite_list = opt.get_optional("tls-ciphersuites", 1, 256);
 
            if (opt.exists("tls-groups"))
                tls_groups = opt.get_optional("tls-groups", 1, 256);
 
            // unsupported cert checkers
            {
            }
        }
 
#ifdef OPENVPN_JSON_INTERNAL
        // The get_string_ref methods require internal JSON and do not work with jsoncpp
        SSLConfigAPI::Ptr json_override(const Json::Value &root, const bool load_cert_key) const override
        {
            static const char title[] = "json_override";
 
            Config::Ptr ret(new Config);
 
            // inherit from self
            ret->mode = mode;
            ret->dh = dh;
            ret->frame = frame;
            ret->flags = flags;
            ret->local_cert_enabled = local_cert_enabled;
 
            // ca
            {
                const std::string &ca_txt = json::get_string_ref(root, "ca", title);
                ret->load_ca(ca_txt, true);
            }
 
            // CRL
            {
                const std::string crl_txt = json::get_string_optional(root, "crl_verify", std::string(), title);
                if (!crl_txt.empty())
                    ret->load_crl(crl_txt);
            }
 
            // cert/key
            if (load_cert_key && local_cert_enabled)
            {
                bool loaded_cert = false;
 
                // cert/extra_certs
                {
                    const std::string cert_txt = json::get_string_optional(root, "cert", std::string(), title);
                    if (!cert_txt.empty())
                    {
                        const std::string ec_txt = json::get_string_optional(root, "extra_certs", std::string(), title);
                        ret->load_cert(cert_txt, ec_txt);
                        loaded_cert = true;
                    }
                    else
                    {
                        ret->cert = cert;
                        ret->extra_certs = extra_certs;
                    }
                }
 
                // private key
                if (loaded_cert && !external_pki)
                {
                    const std::string &key_txt = json::get_string_ref(root, "key", title);
                    if (!key_txt.empty())
                        ret->load_private_key(key_txt);
                    else
                        ret->pkey = pkey;
                }
            }
            else
            {
                // inherit from self
                ret->cert = cert;
                ret->extra_certs = extra_certs;
                ret->pkey = pkey;
            }
 
            // ns_cert_type
            {
                const std::string ct = json::get_string_optional(root, "ns_cert_type", std::string(), title);
                if (!ct.empty())
                    ret->ns_cert_type = NSCert::ns_cert_type(ct);
            }
 
            // ku, eku
            {
                const std::string ct = json::get_string_optional(root, "remote_cert_tls", std::string(), title);
                if (!ct.empty())
                    KUParse::remote_cert_tls(ct, ret->ku, ret->eku);
            }
 
            // tls_version_min
            {
                const std::string tvm = json::get_string_optional(root, "tls_version_min", std::string(), title);
                if (!tvm.empty())
                    ret->tls_version_min = TLSVersion::parse_tls_version_min(tvm, false, maxver());
            }
 
            // tls_cert_profile
            {
                const std::string prof = json::get_string_optional(root, "tls_cert_profile", std::string(), title);
                if (!prof.empty())
                    ret->tls_cert_profile = TLSCertProfile::parse_tls_cert_profile(prof);
            }
 
            return ret;
        }
#endif
 
      private:
        SSLLib::Ctx ctx() const
        {
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
            initialise_lib_context();
            return lib_ctx->ctx();
#else
            return nullptr;
#endif
        }
 
        void initialise_lib_context() const
        {
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
            std::lock_guard guard{lib_ctx_mutex};
 
            if (lib_ctx)
                return;
 
            auto it = lib_ctx_map.find(lib_ctx_provider_config);
 
            if (it != lib_ctx_map.end())
            {
                auto cached_ctx = it->second.lock();
 
                if (cached_ctx)
                {
                    lib_ctx = std::move(cached_ctx);
                    return;
                }
            }
 
            // There's either no cached library context, or the cached context expired.
            lib_ctx = std::make_shared<LibContext>(lib_ctx_provider_config);
            lib_ctx_map[lib_ctx_provider_config] = lib_ctx;
#endif
        }
 
        static TLSVersion::Type maxver()
        {
            // Return maximum TLS version supported by OpenSSL.
            // Assume that presence of SSL_OP_NO_TLSvX macro indicates
            // that local OpenSSL library implements TLSvX.
#ifdef SSL_OP_NO_TLSv1_3
            return TLSVersion::Type::V1_3;
#elif defined(SSL_OP_NO_TLSv1_2)
            return TLSVersion::Type::V1_2;
#elif defined(SSL_OP_NO_TLSv1_1)
            return TLSVersion::Type::V1_1;
#else
            return TLSVersion::Type::V1_0;
#endif
        }
 
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
        /* The C++ standard says:
         *
         * 26.2.6 Associative containers [associative.reqmts]
         *
         * The insert and emplace members shall not affect the validity of iterators
         * and references to the container, and the erase members shall invalidate
         * only iterators and references to the erased elements.
         *
         * So we should be safe to return pointers / references to existing
         * values.
         */
        static inline std::map<unsigned short, std::weak_ptr<LibContext>> lib_ctx_map;
        mutable std::shared_ptr<LibContext> lib_ctx;
        static inline std::mutex lib_ctx_mutex;
#endif
        unsigned short lib_ctx_provider_config{LIB_CTX_NO_PROVIDERS};
 
        Mode mode;
        CertCRLList ca;                   // from OpenVPN "ca" and "crl-verify" option
        OpenSSLPKI::X509 cert;            // from OpenVPN "cert" option
        OpenSSLPKI::X509List extra_certs; // from OpenVPN "extra-certs" option
        OpenSSLPKI::PKey pkey;            // private key
        OpenSSLPKI::DH dh;                // diffie-hellman parameters (only needed in server mode)
        ExternalPKIBase *external_pki = nullptr;
        std::string external_pki_alias;
        TLSSessionTicketBase *session_ticket_handler = nullptr; // server side only
        SNI::HandlerBase *sni_handler = nullptr;                // server side only
        CommonNameReject *cn_reject_handler = nullptr;
        Frame::Ptr frame;
        unsigned int flags = 0; // defined in sslconsts.hpp
        std::string sni_name;   // client side only
        NSCert::Type ns_cert_type{NSCert::NONE};
        std::vector<unsigned int> ku; // if defined, peer cert X509 key usage must match one of these values
        std::string eku;              // if defined, peer cert X509 extended key usage must match this OID/string
        std::string tls_remote;
        VerifyX509Name verify_x509_name;                           // --verify-x509-name feature
        PeerFingerprints peer_fingerprints;                        // --peer-fingerprint
        TLSVersion::Type tls_version_min{TLSVersion::Type::V1_2};  // minimum TLS version that we will negotiate
        TLSVersion::Type tls_version_max{TLSVersion::Type::UNDEF}; // maximum TLS version that we will negotiate, use for testing only (NOT exposed via tls-version-max)
        TLSCertProfile::Type tls_cert_profile{TLSCertProfile::UNDEF};
        std::string tls_cipher_list;
        std::string tls_ciphersuite_list;
        std::string tls_groups;
        X509Track::ConfigSet x509_track_config;
        bool local_cert_enabled = true;
        bool client_session_tickets = false;
    };
 
    // Represents an actual SSL session.
    // Normally instantiated by OpenSSLContext::ssl().
    class SSL : public SSLAPI
    {
        friend class OpenSSLContext;
 
      public:
        using Ptr = RCPtr<SSL>;
 
        void start_handshake() override
        {
            SSL_do_handshake(ssl);
        }
 
        ssize_t write_cleartext_unbuffered(const void *data, const size_t size) override
        {
            const int status = BIO_write(ssl_bio, data, numeric_cast<int>(size));
            if (status < 0)
            {
                if (status == -1 && BIO_should_retry(ssl_bio))
                    return SSLConst::SHOULD_RETRY;
 
                mark_no_cache();
                OPENVPN_THROW(OpenSSLException, "OpenSSLContext::SSL::write_cleartext: BIO_write failed, size=" << size << " status=" << status);
            }
            else
                return status;
        }
 
        ssize_t read_cleartext(void *data, const size_t capacity) override
        {
            if (!overflow)
            {
                const int status = BIO_read(ssl_bio, data, numeric_cast<int>(capacity));
                if (status <= 0)
                {
                    if ((status == 0 || status == -1) && BIO_should_retry(ssl_bio))
                        return SSLConst::SHOULD_RETRY;
 
                    mark_no_cache();
                    OPENVPN_THROW(OpenSSLException, "OpenSSLContext::SSL::read_cleartext: BIO_read failed, cap=" << capacity << " status=" << status);
                }
                else
                    return status;
            }
            else
                throw ssl_ciphertext_in_overflow();
        }
 
        bool read_cleartext_ready() const override
        {
            return !bmq_stream::memq_from_bio(ct_in)->empty() || SSL_pending(ssl) > 0;
        }
 
        void write_ciphertext(const BufferPtr &buf) override
        {
            bmq_stream::MemQ *in = bmq_stream::memq_from_bio(ct_in);
            if (in->size() < MAX_CIPHERTEXT_IN)
                in->write_buf(buf);
            else
                overflow = true;
        }
 
        void write_ciphertext_unbuffered(const unsigned char *data, const size_t size) override
        {
            bmq_stream::MemQ *in = bmq_stream::memq_from_bio(ct_in);
            if (in->size() < MAX_CIPHERTEXT_IN)
                in->write(data, size);
            else
                overflow = true;
        }
 
        bool read_ciphertext_ready() const override
        {
            return !bmq_stream::memq_from_bio(ct_out)->empty();
        }
 
        BufferPtr read_ciphertext() override
        {
            return bmq_stream::memq_from_bio(ct_out)->read_buf();
        }
 
        std::string ssl_handshake_details() const override
        {
            return ssl_handshake_details(ssl);
        }
 
        bool export_keying_material(const std::string &label, unsigned char *dest, size_t size) override
        {
            return SSL_get_session(ssl) && SSL_export_keying_material(ssl, dest, size, label.c_str(), label.size(), nullptr, 0, 0) == 1;
        }
 
        bool did_full_handshake() override
        {
            if (called_did_full_handshake)
                return false;
            called_did_full_handshake = true;
            return !SSL_session_reused(ssl);
        }
 
        const AuthCert::Ptr &auth_cert() const override
        {
            // Reused sessions don't call the cert verify callbacks,
            // so we must use an alternative method to build authcert.
            if (authcert && !authcert->defined())
                rebuild_authcert();
            return authcert;
        }
 
        void mark_no_cache() override
        {
            sess_cache_key.reset();
        }
 
        ~SSL()
        {
            ssl_erase();
        }
 
        static void init_static()
        {
            bmq_stream::init_static();
#if OPENSSL_VERSION_NUMBER < 0x30000010L && !defined(OPENSSL_NO_EC) && defined(ENABLE_EXTERNAL_PKI)
            ExternalPKIECImpl::init_static();
#endif
 
 
            ssl_data_index = SSL_get_ex_new_index(0, (char *)"OpenSSLContext::SSL", nullptr, nullptr, nullptr);
            context_data_index = SSL_get_ex_new_index(0, (char *)"OpenSSLContext", nullptr, nullptr, nullptr);
        }
 
      private:
        SSL(const OpenSSLContext &ctx, const std::string *hostname, const std::string *cache_key)
        {
            ssl_clear();
            try
            {
                // init SSL objects
                ssl = SSL_new(ctx.ctx.get());
                if (!ssl)
                    throw OpenSSLException("OpenSSLContext::SSL: SSL_new failed");
 
                // release unneeded buffers
                SSL_set_mode(ssl, SSL_MODE_RELEASE_BUFFERS);
 
                // verify hostname
                if (hostname && !(ctx.config->flags & SSLConst::NO_VERIFY_HOSTNAME))
                {
                    X509_VERIFY_PARAM *param = SSL_get0_param(ssl);
                    X509_VERIFY_PARAM_set_hostflags(param, 0);
                    X509_VERIFY_PARAM_set1_host(param, hostname->c_str(), 0);
                }
 
                // init BIOs
                ssl_bio = BIO_new(BIO_f_ssl());
                if (!ssl_bio)
                    throw OpenSSLException("OpenSSLContext::SSL: BIO_new BIO_f_ssl failed");
                ct_in = mem_bio(ctx.config->frame);
                ct_out = mem_bio(ctx.config->frame);
 
                // set client/server mode
                if (ctx.config->mode.is_server())
                {
                    SSL_set_accept_state(ssl);
                    authcert.reset(new AuthCert());
                    if (!ctx.config->x509_track_config.empty())
                        authcert->x509_track.reset(new X509Track::Set);
                }
                else if (ctx.config->mode.is_client())
                {
                    if (cache_key && ctx.sess_cache)
                    {
                        // see if a cached session already exists for our cache_key
                        ctx.sess_cache->extract(*cache_key, [this](SSL_SESSION *sess)
                                                {
              if (!SSL_set_session(ssl, sess))
            throw OpenSSLException("SSL_set_session failed"); });
 
                        // cache the session before its end-of-life if no errors occur
                        sess_cache_key.reset(new OpenSSLSessionCache::Key(*cache_key, ctx.sess_cache));
                    }
                    SSL_set_connect_state(ssl);
 
                    // client-side SNI
                    if (!ctx.config->sni_name.empty())
                    {
                        if (SSL_set_tlsext_host_name(ssl, ctx.config->sni_name.c_str()) != 1)
                            throw OpenSSLException("OpenSSLContext::SSL: SSL_set_tlsext_host_name failed (sni_name)");
                    }
                    else if ((ctx.config->flags & SSLConst::ENABLE_CLIENT_SNI) && hostname)
                    {
                        if (SSL_set_tlsext_host_name(ssl, hostname->c_str()) != 1)
                            throw OpenSSLException("OpenSSLContext::SSL: SSL_set_tlsext_host_name failed (hostname)");
                    }
                }
                else
                    OPENVPN_THROW(ssl_context_error, "OpenSSLContext::SSL: unknown client/server mode");
 
                // effect SSL/BIO linkage
                ssl_bio_linkage = true; // after this point, no need to explicitly BIO_free ct_in/ct_out
                SSL_set_bio(ssl, ct_in, ct_out);
                BIO_set_ssl(ssl_bio, ssl, BIO_NOCLOSE);
 
                if (ssl_data_index < 0)
                    throw ssl_context_error("OpenSSLContext::SSL: ssl_data_index is uninitialized");
                SSL_set_ex_data(ssl, ssl_data_index, this);
                set_parent(&ctx);
            }
            catch (...)
            {
                ssl_erase();
                throw;
            }
        }
 
        void set_parent(const OpenSSLContext *ctx)
        {
            if (context_data_index < 0)
                throw ssl_context_error("OpenSSLContext::SSL: context_data_index is uninitialized");
            SSL_set_ex_data(ssl, context_data_index, (void *)ctx);
        }
 
        void rebuild_authcert() const
        {
            ::X509 *cert = SSL_get_peer_certificate(ssl);
            if (cert)
            {
                // save the issuer cert fingerprint
                static_assert(sizeof(AuthCert::issuer_fp) == SHA_DIGEST_LENGTH, "size inconsistency");
 
                unsigned int md_len = sizeof(AuthCert::issuer_fp);
                X509_digest(cert, EVP_sha1(), authcert->issuer_fp, &md_len);
 
                // save the Common Name
                authcert->cn = OpenSSLPKI::x509_get_field(cert, NID_commonName);
 
                // save the leaf cert serial number
                load_serial_number_into_authcert(*authcert, cert);
 
                authcert->defined_ = true;
 
                X509_free(cert);
            }
        }
 
        // Indicate no data available for our custom SSLv23 method
        static int ssl_pending_override(const ::SSL *)
        {
            return 0;
        }
 
        static void print_ec_key_details(EVP_PKEY *pkey, std::ostream &os)
        {
            std::array<char, 1024> gname{};
            size_t gname_sz = gname.size();
 
            const char *group = gname.data();
            if (!EVP_PKEY_get_group_name(pkey, gname.data(), gname_sz, &gname_sz))
            {
                group = "Error getting group name";
            }
            os << ", " << EVP_PKEY_get_bits(pkey) << " bit EC, group:" << group;
        }
 
        // Print a one line summary of SSL/TLS session handshake.
        static std::string ssl_handshake_details(::SSL *ssl)
        {
            std::ostringstream os;
 
            ::X509 *cert = SSL_get_peer_certificate(ssl);
 
            if (cert)
                os << "peer certificate: CN=" << OpenSSLPKI::x509_get_field(cert, NID_commonName);
 
            if (cert != nullptr)
            {
                EVP_PKEY *pkey = X509_get_pubkey(cert);
                if (pkey != nullptr)
                {
#ifndef OPENSSL_NO_EC
                    if ((EVP_PKEY_id(pkey) == EVP_PKEY_EC))
                        print_ec_key_details(pkey, os);
                    else
#endif
                    {
#if OPENSSL_VERSION_NUMBER < 0x30000000L
                        int pkeyId = EVP_PKEY_id(pkey);
                        const char *pkeySN = OBJ_nid2sn(pkeyId);
                        if (!pkeySN)
                            pkeySN = "(error getting public key type)";
 
                        // Nicer names instead of rsaEncryption and dsaEncryption
                        if (pkeyId == EVP_PKEY_RSA)
                            pkeySN = "RSA";
                        else if (pkeyId == EVP_PKEY_DSA)
                            pkeySN = "DSA";
#else  /* OpenSSL >= 3 */
                        const char *pkeySN = EVP_PKEY_get0_type_name(pkey);
                        if (!pkeySN)
                        {
                            pkeySN = "(error getting public key type)";
                        }
#endif /* if OPENSSL_VERSION_NUMBER < 0x30000000L */
 
                        os << ", " << EVP_PKEY_bits(pkey) << " bit " << pkeySN;
                    }
                    EVP_PKEY_free(pkey);
                }
                X509_free(cert);
            }
 
            const SSL_CIPHER *ciph = SSL_get_current_cipher(ssl);
            if (ciph)
            {
                char *desc = SSL_CIPHER_description(ciph, nullptr, 0);
                if (!desc)
                {
                    os << ", cipher: Error getting TLS cipher description from SSL_CIPHER_description";
                }
                else
                {
                    std::string cipher_str(desc);
                    // remove \n at the end and any other excess whitespace
                    string::trim(cipher_str);
                    os << ", cipher: " << cipher_str;
                    OPENSSL_free(desc);
                }
            }
 
            if (SSL_session_reused(ssl))
                os << " [REUSED]";
 
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
            const char *key_agreement = SSL_get0_group_name(ssl);
            if (!key_agreement)
            {
                key_agreement = "(error fetching key-agreeement)";
            }
            os << ", key-agreement: " << key_agreement;
#endif
 
            return os.str();
        }
 
        void ssl_clear()
        {
            ssl_bio_linkage = false;
            ssl = nullptr;
            ssl_bio = nullptr;
            ct_in = nullptr;
            ct_out = nullptr;
            overflow = false;
            called_did_full_handshake = false;
            sess_cache_key.reset();
        }
 
        void ssl_erase()
        {
            if (!ssl_bio_linkage)
            {
                if (ct_in)
                    BIO_free(ct_in);
                if (ct_out)
                    BIO_free(ct_out);
            }
 
            BIO_free_all(ssl_bio);
            if (sess_cache_key)
            {
                SSL_set_shutdown(ssl, SSL_SENT_SHUTDOWN | SSL_RECEIVED_SHUTDOWN);
                sess_cache_key->commit(SSL_get1_session(ssl));
            }
            SSL_free(ssl);
            openssl_clear_error_stack();
            ssl_clear();
        }
 
        static BIO *mem_bio(const Frame::Ptr &frame)
        {
            BIO *bio = BIO_new(bmq_stream::BIO_s_memq());
            if (!bio)
                throw OpenSSLException("OpenSSLContext::SSL: BIO_new failed on bmq_stream");
            bmq_stream::memq_from_bio(bio)->set_frame(frame);
            return bio;
        }
 
        ::SSL *ssl;   // OpenSSL SSL object
        BIO *ssl_bio; // read/write cleartext from here
        BIO *ct_in;   // write ciphertext to here
        BIO *ct_out;  // read ciphertext from here
        AuthCert::Ptr authcert;
        OpenSSLSessionCache::Key::UPtr sess_cache_key; // client-side only
        OpenSSLContext::Ptr sni_ctx;
        bool ssl_bio_linkage;
        bool overflow;
        bool called_did_full_handshake;
 
        // Helps us to store pointer to self in ::SSL object
        inline static int ssl_data_index = -1;
        inline static int context_data_index = -1;
    };
 
    static std::string translate_cipher_list(const std::string &cipherlist)
    {
        // OpenVPN 2.x accepts IANA ciphers instead in the cipher list, we need
        // to do the same
 
        std::stringstream cipher_list_ss(cipherlist);
        std::string ciphersuite;
 
        std::stringstream result;
 
 
        while (std::getline(cipher_list_ss, ciphersuite, ':'))
        {
            const tls_cipher_name_pair *pair = tls_get_cipher_name_pair(ciphersuite);
 
            if (!result.str().empty())
                result << ":";
 
            if (pair)
            {
                if (pair->iana_name != ciphersuite)
                {
                    OVPN_LOG_INFO("OpenSSLContext: Deprecated cipher suite name '"
                                  << pair->openssl_name << "' please use IANA name ' "
                                  << pair->iana_name << "'");
                }
                result << pair->openssl_name;
            }
            else
            {
                result << ciphersuite;
            }
        }
 
        return result.str();
    }
 
  private:
    void setup_server_ticket_callback() const
    {
        const std::string sess_id_context = config->session_ticket_handler->session_id_context();
        if (!SSL_CTX_set_session_id_context(ctx.get(), (unsigned char *)sess_id_context.c_str(), numeric_cast<unsigned int>(sess_id_context.length())))
            throw OpenSSLException("OpenSSLContext: SSL_CTX_set_session_id_context failed");
 
#if OPENSSL_VERSION_NUMBER < 0x30000000L
        if (!SSL_CTX_set_tlsext_ticket_key_cb(ctx.get(), tls_ticket_key_callback))
            throw OpenSSLException("OpenSSLContext: SSL_CTX_set_tlsext_ticket_key_cb failed");
#else
 
        if (!SSL_CTX_set_tlsext_ticket_key_evp_cb(ctx.get(), tls_ticket_key_callback))
            throw OpenSSLException("OpenSSLContext: SSL_CTX_set_tlsext_ticket_evp_cb failed");
#endif
    }
 
    OpenSSLContext(Config *config_arg)
        : config(config_arg)
    {
        // Create new SSL_CTX for server or client mode
        if (config->mode.is_server())
        {
            ctx = SSL_CTX_unique_ptr{SSL_CTX_new_ex(libctx(), nullptr, ::TLS_server_method()), ::SSL_CTX_free};
            if (!ctx)
                throw OpenSSLException("OpenSSLContext: SSL_CTX_new_ex failed for server method");
 
            // Set DH object
            if (config->dh.defined())
            {
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
                if (!SSL_CTX_set0_tmp_dh_pkey(ctx.get(), config->dh.obj_release()))
                    throw OpenSSLException("OpenSSLContext: SSL_CTX_set0_tmp_dh_pkey failed");
#else
                if (!SSL_CTX_set_tmp_dh(ctx.get(), config->dh.obj()))
                    throw OpenSSLException("OpenSSLContext: SSL_CTX_set_tmp_dh failed");
#endif
            }
            if (config->flags & SSLConst::SERVER_TO_SERVER)
                SSL_CTX_set_purpose(ctx.get(), X509_PURPOSE_SSL_SERVER);
 
            // server-side SNI
            if (config->sni_handler)
            {
                SSL_CTX_set_client_hello_cb(ctx.get(), client_hello_callback, nullptr);
            }
        }
        else if (config->mode.is_client())
        {
            ctx = SSL_CTX_unique_ptr{SSL_CTX_new_ex(libctx(), nullptr, ::TLS_client_method()), &::SSL_CTX_free};
            if (!ctx)
                throw OpenSSLException("OpenSSLContext: SSL_CTX_new_ex failed for client method");
        }
        else
            OPENVPN_THROW(ssl_context_error, "OpenSSLContext: unknown config->mode");
 
        // Set SSL options
        if (!(config->flags & SSLConst::NO_VERIFY_PEER))
        {
            int vf = SSL_VERIFY_PEER;
            if (!(config->flags & SSLConst::PEER_CERT_OPTIONAL))
                vf |= SSL_VERIFY_FAIL_IF_NO_PEER_CERT;
            SSL_CTX_set_verify(ctx.get(),
                               vf,
                               config->mode.is_client()
                                   ? verify_callback_client
                                   : verify_callback_server);
            SSL_CTX_set_verify_depth(ctx.get(), 16);
        }
 
        /* Disable SSLv2 and SSLv3, might be a noop but does not hurt */
        long sslopt = SSL_OP_SINGLE_DH_USE | SSL_OP_SINGLE_ECDH_USE | SSL_OP_NO_COMPRESSION | SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3;
 
#ifdef SSL_OP_NO_RENEGOTIATION
        sslopt |= SSL_OP_NO_RENEGOTIATION;
#endif
 
        if (config->mode.is_server())
        {
            SSL_CTX_set_session_cache_mode(ctx.get(), SSL_SESS_CACHE_OFF);
            if (config->session_ticket_handler)
            {
                setup_server_ticket_callback();
            }
            else
                sslopt |= SSL_OP_NO_TICKET;
 
            // send a client CA list to the client
            if (config->flags & SSLConst::SEND_CLIENT_CA_LIST)
            {
                for (const auto &e : config->ca.certs)
                {
                    if (SSL_CTX_add_client_CA(ctx.get(), e.obj()) != 1)
                        throw OpenSSLException("OpenSSLContext: SSL_CTX_add_client_CA failed");
                }
            }
        }
        else
        {
            if (config->client_session_tickets)
            {
                SSL_CTX_set_session_cache_mode(ctx.get(), SSL_SESS_CACHE_CLIENT);
                sess_cache.reset(new OpenSSLSessionCache);
            }
            else
            {
                SSL_CTX_set_session_cache_mode(ctx.get(), SSL_SESS_CACHE_OFF);
                sslopt |= SSL_OP_NO_TICKET;
            }
        }
#if OPENSSL_VERSION_NUMBER >= 0x10100000L
        if (config->tls_version_min > TLSVersion::Type::V1_0)
        {
            SSL_CTX_set_min_proto_version(ctx.get(), TLSVersion::toTLSVersion(config->tls_version_min));
        }
#else
        if (config->tls_version_min > TLSVersion::Type::V1_0)
            sslopt |= SSL_OP_NO_TLSv1;
#ifdef SSL_OP_NO_TLSv1_1
        if (config->tls_version_min > TLSVersion::Type::V1_1)
            sslopt |= SSL_OP_NO_TLSv1_1;
#endif
#ifdef SSL_OP_NO_TLSv1_2
        if (config->tls_version_min > TLSVersion::Type::V1_2)
            sslopt |= SSL_OP_NO_TLSv1_2;
#endif
#ifdef SSL_OP_NO_TLSv1_3
        if (config->tls_version_min > TLSVersion::Type::V1_3)
            sslopt |= SSL_OP_NO_TLSv1_3;
#endif
#endif
#if OPENSSL_VERSION_NUMBER >= 0x10100000L
        if (config->tls_version_max != TLSVersion::Type::UNDEF)
        {
            SSL_CTX_set_max_proto_version(ctx.get(), TLSVersion::toTLSVersion(config->tls_version_max));
        }
#else
        if (config->tls_version_max < TLSVersion::Type::V1_0)
            sslopt |= SSL_OP_NO_TLSv1;
#ifdef SSL_OP_NO_TLSv1_1
        if (config->tls_version_max < TLSVersion::Type::V1_1)
            sslopt |= SSL_OP_NO_TLSv1_1;
#endif
#ifdef SSL_OP_NO_TLSv1_2
        if (config->tls_version_max < TLSVersion::Type::V1_2)
            sslopt |= SSL_OP_NO_TLSv1_2;
#endif
#ifdef SSL_OP_NO_TLSv1_3
        if (config->tls_version_max < TLSVersion::Type::V1_3)
            sslopt |= SSL_OP_NO_TLSv1_3;
#endif
#endif
        SSL_CTX_set_options(ctx.get(), sslopt);
 
        if (!config->tls_groups.empty())
        {
            set_openssl_tls_groups(config->tls_groups);
        }
#ifdef TLS1_3_VERSION
        if (!config->tls_ciphersuite_list.empty())
        {
            if (!SSL_CTX_set_ciphersuites(ctx.get(), config->tls_ciphersuite_list.c_str()))
                OPENVPN_THROW(ssl_context_error, "OpenSSLContext: SSL_CTX_set_ciphersuites_list failed");
        }
#endif
        std::string tls_cipher_list =
            /* default list as a basis */
            "DEFAULT"
            /* Disable export ciphers, low and medium */
            ":!EXP:!LOW:!MEDIUM"
            /* Disable static (EC)DH keys (no forward secrecy) */
            ":!kDH:!kECDH"
            /* Disable DSA private keys */
            ":!DSS"
            /* Disable RC4 cipher */
            ":!RC4"
            /* Disable MD5 */
            ":!MD5"
            /* Disable unsupported TLS modes */
            ":!PSK:!SRP:!kRSA"
            /* Disable SSLv2 cipher suites*/
            ":!SSLv2";
 
        /* If we are using preferred, we also do not want to allow SHA1
         * cipher suites. This is also included in security level 4 of
         * OpenSSL*/
        if (TLSCertProfile::default_if_undef(config->tls_cert_profile) >= TLSCertProfile::PREFERRED)
            tls_cipher_list += ":!SHA1";
 
        if (!config->tls_cipher_list.empty())
        {
            tls_cipher_list = translate_cipher_list(config->tls_cipher_list);
        }
 
        if (!SSL_CTX_set_cipher_list(ctx.get(), tls_cipher_list.c_str()))
            OPENVPN_THROW(ssl_context_error, "OpenSSLContext: SSL_CTX_set_cipher_list failed");
#if OPENSSL_VERSION_NUMBER >= 0x10002000L && OPENSSL_VERSION_NUMBER < 0x10100000L
        SSL_CTX_set_ecdh_auto(ctx.get(), 1); // this method becomes a no-op in OpenSSL 1.1
#endif
 
#if OPENSSL_VERSION_NUMBER >= 0x10100000L
        switch (TLSCertProfile::default_if_undef(config->tls_cert_profile))
        {
        case TLSCertProfile::UNDEF:
            OPENVPN_THROW(ssl_context_error,
                          "OpenSSLContext: undefined tls-cert-profile");
            break;
#ifdef OPENVPN_ALLOW_INSECURE_CERTPROFILE
        case TLSCertProfile::INSECURE:
            SSL_CTX_set_security_level(ctx.get(), 0);
            break;
#endif
        case TLSCertProfile::LEGACY:
            SSL_CTX_set_security_level(ctx.get(), 1);
            break;
        case TLSCertProfile::PREFERRED:
            SSL_CTX_set_security_level(ctx.get(), 2);
            break;
        case TLSCertProfile::SUITEB:
            SSL_CTX_set_security_level(ctx.get(), 3);
            break;
        default:
            OPENVPN_THROW(ssl_context_error,
                          "OpenSSLContext: unexpected tls-cert-profile value");
            break;
        }
#else
        // when OpenSSL does not CertProfile support we force the user to set 'legacy'
        if (TLSCertProfile::default_if_undef(config->tls_cert_profile) != TLSCertProfile::LEGACY)
        {
            OPENVPN_THROW(ssl_context_error,
                          "OpenSSLContext: tls-cert-profile not supported by this OpenSSL build. Use 'legacy' instead");
        }
#endif
 
        if (config->local_cert_enabled)
        {
            // Set certificate
            if (!config->cert.defined())
                OPENVPN_THROW(ssl_context_error, "OpenSSLContext: cert not defined");
            if (SSL_CTX_use_certificate(ctx.get(), config->cert.obj()) != 1)
                throw OpenSSLException("OpenSSLContext: SSL_CTX_use_certificate failed");
 
            // Set private key
            if (config->external_pki)
            {
#ifdef ENABLE_EXTERNAL_PKI
#if OPENSSL_VERSION_NUMBER >= 0x30000010L
                epki = XKeyExternalPKIImpl::create(ctx.get(), config->cert.obj(), config->external_pki, config->external_pki_alias);
 
#else
                auto certType = EVP_PKEY_id(X509_get0_pubkey(config->cert.obj()));
                if (certType == EVP_PKEY_RSA)
                {
                    epki = std::make_shared<ExternalPKIImpl>(ExternalPKIRsaImpl(ctx.get(), config->cert.obj(), config->external_pki, config->external_pki_alias));
                }
#if OPENSSL_VERSION_NUMBER >= 0x10100000L && !defined(OPENSSL_NO_EC)
                else if (certType == EVP_PKEY_EC)
                {
                    epki = std::make_shared<ExternalPKIImpl>(ExternalPKIECImpl(ctx.get(), config->cert.obj(), config->external_pki, config->external_pki_alias));
                }
#endif
                else
                {
                    throw OpenSSLException("OpenSSLContext: pkey is neither RSA nor EC. Unsupported with external pki");
                }
#endif
#else
                throw OpenSSLException("OpenSSLContext: External PKI is not enabled in this build. ");
#endif
            }
            else
            {
                if (!config->pkey.defined())
                    OPENVPN_THROW(ssl_context_error, "OpenSSLContext: private key not defined");
                if (SSL_CTX_use_PrivateKey(ctx.get(), config->pkey.obj()) != 1)
                    throw OpenSSLException("OpenSSLContext: SSL_CTX_use_PrivateKey failed");
 
                // Check cert/private key compatibility
                if (!SSL_CTX_check_private_key(ctx.get()))
                    throw OpenSSLException("OpenSSLContext: private key does not match the certificate");
            }
 
            // Set extra certificates that are part of our own certificate
            // chain but shouldn't be included in the verify chain.
            if (config->extra_certs.defined())
            {
                for (const auto &e : config->extra_certs)
                {
                    if (SSL_CTX_add_extra_chain_cert(ctx.get(), e.obj_dup()) != 1)
                        throw OpenSSLException("OpenSSLContext: SSL_CTX_add_extra_chain_cert failed");
                }
            }
        }
 
        // Set CAs/CRLs
        if (config->ca.certs.defined())
            update_trust(config->ca);
        else if (!(config->flags & (SSLConst::NO_VERIFY_PEER | SSLConst::VERIFY_PEER_FINGERPRINT)))
            OPENVPN_THROW(ssl_context_error, "OpenSSLContext: CA not defined");
 
        // Show handshake debugging info
        if (log_.log_level() >= logging::LOG_LEVEL_INFO)
            SSL_CTX_set_info_callback(ctx.get(), info_callback);
    }
 
  public:
    // create a new SSL instance
    SSLAPI::Ptr ssl() override
    {
        return SSL::Ptr(new SSL(*this, nullptr, nullptr));
    }
 
    // like ssl() above but verify hostname against cert CommonName and/or SubjectAltName
    SSLAPI::Ptr ssl(const std::string *hostname, const std::string *cache_key) override
    {
        return SSL::Ptr(new SSL(*this, hostname, cache_key));
    }
 
    SSLLib::Ctx libctx() override
    {
        SSLLib::Ctx lib_ctx = config->ctx();
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
        if (!lib_ctx)
            throw OpenSSLException("OpenSSLContext: library context is not initialised");
#endif
        return lib_ctx;
    }
 
 
    void update_trust(const CertCRLList &cc)
    {
        OpenSSLPKI::X509Store store(cc);
        SSL_CTX_set_cert_store(ctx.get(), store.release());
    }
 
    ~OpenSSLContext() = default;
 
    const Mode &mode() const override
    {
        return config->mode;
    }
 
    constexpr static bool support_key_material_export()
    {
        return true;
    }
 
#ifdef UNIT_TEST
    static void load_cert_info_into_authcert(AuthCert &authcert, const std::string &cert_txt)
    {
        const OpenSSLPKI::X509 cert(cert_txt, "OpenSSLContext::load_cert_info_into_authcert");
 
        // save the issuer cert fingerprint
        {
            unsigned int md_len = sizeof(AuthCert::issuer_fp);
            X509_digest(cert.obj(), EVP_sha1(), authcert.issuer_fp, &md_len);
        }
 
        // save the Common Name
        authcert.cn = OpenSSLPKI::x509_get_field(cert.obj(), NID_commonName);
 
        // save the cert serial number
        load_serial_number_into_authcert(authcert, cert.obj());
 
        authcert.defined_ = true;
    }
#endif
 
  private:
    // ns-cert-type verification
 
    bool ns_cert_type_defined() const
    {
        return config->ns_cert_type != NSCert::NONE;
    }
 
    bool verify_ns_cert_type(::X509 *cert) const
    {
        if (config->ns_cert_type == NSCert::SERVER)
            return X509_check_purpose(cert, X509_PURPOSE_SSL_SERVER, 0);
        if (config->ns_cert_type == NSCert::CLIENT)
            return X509_check_purpose(cert, X509_PURPOSE_SSL_CLIENT, 0);
        return true;
    }
 
 
    void set_openssl_tls_groups(const std::string &tls_groups)
    {
        auto num_groups = std::count(tls_groups.begin(), tls_groups.end(), ':') + 1;
 
        std::unique_ptr<int[]> glist(new int[num_groups]);
 
        std::stringstream groups_ss(tls_groups);
        std::string group;
 
        int glistlen = 0;
        while (std::getline(groups_ss, group, ':'))
        {
            /* Dance around that the fact that even though OpenSSL authors
             * call this group secp256r1 in their own source code, OpenSSL
             * externally only knows this by prime256v1 or P-256 */
            if (group == "secp256r1")
            {
                group = "prime256v1";
            }
 
            int nid = OBJ_sn2nid(group.c_str());
            if (nid != 0)
            {
                glist[glistlen] = nid;
                glistlen++;
            }
            else
            {
                OVPN_LOG_INFO("OpenSSL -- warning ignoring unknown group '"
                              << group << "' in tls-groups");
            }
        }
 
        if (!SSL_CTX_set1_groups(ctx.get(), glist.get(), glistlen))
            OPENVPN_THROW(ssl_context_error, "OpenSSLContext: SSL_CTX_set1_groups failed");
    }
 
    // remote-cert-ku verification
 
    bool x509_cert_ku_defined() const
    {
        return !config->ku.empty();
    }
 
    bool verify_x509_cert_ku(::X509 *cert) const
    {
        bool found = false;
        ASN1_BIT_STRING *ku = (ASN1_BIT_STRING *)X509_get_ext_d2i(cert, NID_key_usage, nullptr, nullptr);
 
        if (ku)
        {
            // Extract key usage bits
            unsigned int nku = 0;
            {
                for (int i = 0; i < 8; i++)
                {
                    if (ASN1_BIT_STRING_get_bit(ku, i))
                        nku |= 1 << (7 - i);
                }
            }
 
            // Fixup if no LSB bits
            if ((nku & 0xff) == 0)
                nku >>= 8;
 
            // Validating certificate key usage
            {
                for (std::vector<unsigned int>::const_iterator i = config->ku.begin(); i != config->ku.end(); ++i)
                {
                    if (nku == *i)
                    {
                        found = true;
                        break;
                    }
                }
            }
 
            ASN1_BIT_STRING_free(ku);
        }
        return found;
    }
 
    // remote-cert-eku verification
 
    bool x509_cert_eku_defined() const
    {
        return !config->eku.empty();
    }
 
    bool verify_x509_cert_eku(::X509 *cert) const
    {
        bool found = false;
        EXTENDED_KEY_USAGE *eku = (EXTENDED_KEY_USAGE *)X509_get_ext_d2i(cert, NID_ext_key_usage, nullptr, nullptr);
 
        if (eku)
        {
            // Validating certificate extended key usage
            for (int i = 0; !found && i < sk_ASN1_OBJECT_num(eku); i++)
            {
                ASN1_OBJECT *oid = sk_ASN1_OBJECT_value(eku, i);
                char oid_str[256];
 
                if (!found && OBJ_obj2txt(oid_str, sizeof(oid_str), oid, 0) != -1)
                {
                    // Compare EKU against string
                    if (config->eku == oid_str)
                        found = true;
                }
 
                if (!found && OBJ_obj2txt(oid_str, sizeof(oid_str), oid, 1) != -1)
                {
                    // Compare EKU against OID
                    if (config->eku == oid_str)
                        found = true;
                }
            }
 
            sk_ASN1_OBJECT_pop_free(eku, ASN1_OBJECT_free);
        }
        return found;
    }
 
    static void x509_track_extract_nid(const X509Track::Type xt_type,
                                       const int nid,
                                       ::X509 *cert,
                                       const int depth,
                                       X509Track::Set &xts)
    {
        const std::string value = OpenSSLPKI::x509_get_field(cert, nid);
        if (!value.empty())
            xts.emplace_back(xt_type, depth, OpenSSLPKI::x509_get_field(cert, nid));
    }
 
    static void x509_track_extract_from_cert(::X509 *cert,
                                             const int depth,
                                             const X509Track::ConfigSet &cs,
                                             X509Track::Set &xts)
    {
        for (auto &c : cs)
        {
            if (c.depth_match(depth))
            {
                switch (c.type)
                {
                case X509Track::SERIAL:
                    {
                        std::string serial = OpenSSLPKI::x509_get_serial(cert);
                        if (!serial.empty())
                            xts.emplace_back(X509Track::SERIAL,
                                             depth,
                                             serial);
                    }
                    break;
                case X509Track::SERIAL_HEX:
                    xts.emplace_back(X509Track::SERIAL_HEX,
                                     depth,
                                     OpenSSLPKI::x509_get_serial_hex(cert));
                    break;
                case X509Track::SHA1:
                    {
                        unsigned char buf[EVP_MAX_MD_SIZE];
                        unsigned int len = EVP_MAX_MD_SIZE;
                        X509_digest(cert, EVP_sha1(), buf, &len);
                        xts.emplace_back(X509Track::SHA1,
                                         depth,
                                         render_hex_sep(buf, len, ':', true));
                    }
                    break;
                case X509Track::CN:
                    x509_track_extract_nid(X509Track::CN, NID_commonName, cert, depth, xts);
                    break;
                case X509Track::C:
                    x509_track_extract_nid(X509Track::C, NID_countryName, cert, depth, xts);
                    break;
                case X509Track::L:
                    x509_track_extract_nid(X509Track::L, NID_localityName, cert, depth, xts);
                    break;
                case X509Track::ST:
                    x509_track_extract_nid(X509Track::ST, NID_stateOrProvinceName, cert, depth, xts);
                    break;
                case X509Track::O:
                    x509_track_extract_nid(X509Track::O, NID_organizationName, cert, depth, xts);
                    break;
                case X509Track::OU:
                    x509_track_extract_nid(X509Track::OU, NID_organizationalUnitName, cert, depth, xts);
                    break;
                case X509Track::EMAIL:
                    x509_track_extract_nid(X509Track::EMAIL, NID_pkcs9_emailAddress, cert, depth, xts);
                    break;
                default:
                    break;
                }
            }
        }
    }
 
    static void load_serial_number_into_authcert(AuthCert &authcert, ::X509 *cert)
    {
        const ASN1_INTEGER *ai = X509_get_serialNumber(cert);
        if (!ai)
            return;
        if (ai->type == V_ASN1_NEG_INTEGER) // negative serial number is considered to be undefined
            return;
        if (!is_safe_conversion<int>(authcert.serial.size()))
            return;
        BIGNUM *bn = ASN1_INTEGER_to_BN(ai, NULL);
        if (!bn)
            return;
 
        BN_bn2binpad(bn, authcert.serial.number(), static_cast<int>(authcert.serial.size()));
        BN_free(bn);
    }
 
    static std::string cert_status_line(int preverify_ok,
                                        int depth,
                                        int err,
                                        const std::string &signature,
                                        const std::string &subject)
    {
        std::string ret;
        ret.reserve(128);
        ret = "VERIFY";
        if (preverify_ok)
            ret += " OK";
        else
            ret += " FAIL";
        ret += ": depth=";
        ret += openvpn::to_string(depth);
        ret += ", ";
        if (!subject.empty())
            ret += subject;
        else
            ret += "NO_SUBJECT";
        ret += ", signature: " + signature;
        if (!preverify_ok)
        {
            ret += " [";
            ret += X509_verify_cert_error_string(err);
            ret += ']';
        }
        return ret;
    }
 
    static AuthCert::Fail::Type cert_fail_code(const int openssl_err)
    {
        // NOTE: this method should never return OK
        switch (openssl_err)
        {
        case X509_V_ERR_CERT_HAS_EXPIRED:
            return AuthCert::Fail::EXPIRED;
        default:
            return AuthCert::Fail::CERT_FAIL;
        }
    }
 
 
    static int check_cert_warnings(const X509 *cert)
    {
        int nid = X509_get_signature_nid(cert);
 
        switch (nid)
        {
        case NID_ecdsa_with_SHA1:
        case NID_dsaWithSHA:
        case NID_dsaWithSHA1:
        case NID_sha1WithRSAEncryption:
            return SSLAPI::TLS_WARN_SIG_SHA1;
        case NID_md5WithRSA:
        case NID_md5WithRSAEncryption:
            return SSLAPI::TLS_WARN_SIG_MD5;
        default:
            return SSLAPI::TLS_WARN_NONE;
        }
    }
 
    static int verify_callback_client(int preverify_ok, X509_STORE_CTX *ctx)
    {
        // get the OpenSSL SSL object
        ::SSL *ssl = (::SSL *)X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
 
        // get OpenSSLContext
        const OpenSSLContext *self = (OpenSSLContext *)SSL_get_ex_data(ssl, SSL::context_data_index);
 
        // get OpenSSLContext::SSL
        SSL *self_ssl = (SSL *)SSL_get_ex_data(ssl, SSL::ssl_data_index);
 
        // get depth
        const int depth = X509_STORE_CTX_get_error_depth(ctx);
 
        // get current certificate
        X509 *current_cert = X509_STORE_CTX_get_current_cert(ctx);
 
        // log subject
        const std::string subject = OpenSSLPKI::x509_get_subject(current_cert);
        if (self->config->flags & SSLConst::LOG_VERIFY_STATUS)
        {
            // don't log self-signed leaf-cert errors with peer-fingerprint validation
            int err = X509_STORE_CTX_get_error(ctx);
            if (preverify_ok
                || err != X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT
                || !(self->config->flags & SSLConst::VERIFY_PEER_FINGERPRINT))
            {
                auto sign_alg = OpenSSLPKI::x509_get_signature_algorithm(current_cert);
                OVPN_LOG_INFO(cert_status_line(preverify_ok, depth, err, sign_alg, subject));
                // Output the certificates itself for debug logging
                OVPN_LOG_TRACE(OpenSSLPKI::X509_get_pem_encoding(current_cert));
            }
        }
 
        // Add warnings if Cert parameters are wrong
        self_ssl->tls_warnings |= self->check_cert_warnings(current_cert);
 
        // If a verification error occured in the certificate chain, we
        // never override the result of the verification.
        if (depth != 0)
            return preverify_ok;
 
        // peer-fingerprint
        PeerFingerprint fp(OpenSSLPKI::x509_get_fingerprint(current_cert));
        if (self->config->peer_fingerprints)
        {
            // might override the OpenSSL verification result to "true"
            // since we only care about the fingerprint and not the
            // certificate chain.
            preverify_ok = self->config->peer_fingerprints.match(fp);
            if (!preverify_ok)
            {
                OVPN_LOG_INFO("VERIFY FAIL -- bad peer-fingerprint in leaf certificate");
            }
        }
 
        // verify ns-cert-type
        if (self->ns_cert_type_defined() && !self->verify_ns_cert_type(current_cert))
        {
            OVPN_LOG_INFO("VERIFY FAIL -- bad ns-cert-type in leaf certificate");
            preverify_ok = false;
        }
 
        // verify X509 key usage
        if (self->x509_cert_ku_defined() && !self->verify_x509_cert_ku(current_cert))
        {
            OVPN_LOG_INFO("VERIFY FAIL -- bad X509 key usage in leaf certificate");
            preverify_ok = false;
        }
 
        // verify X509 extended key usage
        if (self->x509_cert_eku_defined() && !self->verify_x509_cert_eku(current_cert))
        {
            OVPN_LOG_INFO("VERIFY FAIL -- bad X509 extended key usage in leaf certificate");
            preverify_ok = false;
        }
 
        // verify-x509-name
        const VerifyX509Name &verify_x509 = self->config->verify_x509_name;
        if (verify_x509.get_mode() != VerifyX509Name::VERIFY_X509_NONE)
        {
            std::string name;
            if (verify_x509.get_mode() == VerifyX509Name::VERIFY_X509_SUBJECT_DN)
                name = OpenSSLPKI::x509_get_subject(current_cert, true);
            else
                name = OpenSSLPKI::x509_get_field(current_cert, NID_commonName);
 
            if (!verify_x509.verify(name))
            {
                OVPN_LOG_INFO("VERIFY FAIL -- verify-x509-name failed");
                preverify_ok = false;
            }
        }
 
        // verify tls-remote
        if (!self->config->tls_remote.empty())
        {
            const std::string subj = TLSRemote::sanitize_x509_name(subject);
            const std::string common_name = TLSRemote::sanitize_common_name(OpenSSLPKI::x509_get_field(current_cert, NID_commonName));
            TLSRemote::log(self->config->tls_remote, subj, common_name);
            if (!TLSRemote::test(self->config->tls_remote, subj, common_name))
            {
                OVPN_LOG_INFO("VERIFY FAIL -- tls-remote match failed");
                preverify_ok = false;
            }
        }
 
        return preverify_ok;
    }
 
    static int verify_callback_server(int preverify_ok, X509_STORE_CTX *ctx)
    {
        // get the OpenSSL SSL object
        ::SSL *ssl = (::SSL *)X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
 
        // get OpenSSLContext
        const OpenSSLContext *self = (OpenSSLContext *)SSL_get_ex_data(ssl, SSL::context_data_index);
 
        // get OpenSSLContext::SSL
        SSL *self_ssl = (SSL *)SSL_get_ex_data(ssl, SSL::ssl_data_index);
 
        // get error code
        const int err = X509_STORE_CTX_get_error(ctx);
 
        // get depth
        const int depth = X509_STORE_CTX_get_error_depth(ctx);
 
        // get current certificate
        X509 *current_cert = X509_STORE_CTX_get_current_cert(ctx);
 
        // log subject
        if (self->config->flags & SSLConst::LOG_VERIFY_STATUS)
        {
            // don't log self-signed leaf-cert errors with peer-fingerprint validation
            int err = X509_STORE_CTX_get_error(ctx);
            if (preverify_ok
                || err != X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT
                || !(self->config->flags & SSLConst::VERIFY_PEER_FINGERPRINT))
            {
                const auto sign_alg = OpenSSLPKI::x509_get_signature_algorithm(current_cert);
                const auto subject = OpenSSLPKI::x509_get_subject(current_cert);
                OVPN_LOG_INFO(cert_status_line(preverify_ok, depth, err, sign_alg, subject));
            }
        }
 
        // record cert error in authcert
        if (!preverify_ok && self_ssl->authcert)
            self_ssl->authcert->add_fail(depth,
                                         cert_fail_code(err),
                                         X509_verify_cert_error_string(err));
 
        // Note on X509_STORE_CTX_set_error: see ssl/statem/statem_lib.c in
        // OpenSSL source for mapping from X509_STORE_CTX_set_error() codes
        // to TLS alert codes.
        if (depth == 1) // issuer cert
        {
            // save the issuer cert fingerprint
            if (self_ssl->authcert)
            {
                static_assert(sizeof(AuthCert::issuer_fp) == SHA_DIGEST_LENGTH, "size inconsistency");
                unsigned int digest_len = sizeof(AuthCert::issuer_fp);
                if (!X509_digest(current_cert, EVP_sha1(), self_ssl->authcert->issuer_fp, &digest_len))
                    preverify_ok = false;
            }
        }
        else if (depth == 0) // leaf cert
        {
            // peer-fingerprint
            PeerFingerprint fp(OpenSSLPKI::x509_get_fingerprint(current_cert));
            if (self->config->peer_fingerprints && !self->config->peer_fingerprints.match(fp))
            {
                OVPN_LOG_INFO("VERIFY FAIL -- bad peer-fingerprint in leaf certificate");
                if (self_ssl->authcert)
                    self_ssl->authcert->add_fail(depth,
                                                 AuthCert::Fail::BAD_CERT_TYPE,
                                                 "bad peer-fingerprint in leaf certificate");
                X509_STORE_CTX_set_error(ctx, X509_V_ERR_UNABLE_TO_VERIFY_LEAF_SIGNATURE); // alert code: SSL_R_TLSV1_ALERT_UNKNOWN_CA
                preverify_ok = false;
            }
 
            // verify ns-cert-type
            if (self->ns_cert_type_defined() && !self->verify_ns_cert_type(current_cert))
            {
                OVPN_LOG_INFO("VERIFY FAIL -- bad ns-cert-type in leaf certificate");
                if (self_ssl->authcert)
                    self_ssl->authcert->add_fail(depth,
                                                 AuthCert::Fail::BAD_CERT_TYPE,
                                                 "bad ns-cert-type in leaf certificate");
                X509_STORE_CTX_set_error(ctx, X509_V_ERR_INVALID_PURPOSE); // alert code: SSL_R_SSLV3_ALERT_UNSUPPORTED_CERTIFICATE
                preverify_ok = false;
            }
 
            // verify X509 key usage
            if (self->x509_cert_ku_defined() && !self->verify_x509_cert_ku(current_cert))
            {
                OVPN_LOG_INFO("VERIFY FAIL -- bad X509 key usage in leaf certificate");
                if (self_ssl->authcert)
                    self_ssl->authcert->add_fail(depth,
                                                 AuthCert::Fail::BAD_CERT_TYPE,
                                                 "bad X509 key usage in leaf certificate");
                X509_STORE_CTX_set_error(ctx, X509_V_ERR_INVALID_PURPOSE); // alert code: SSL_R_SSLV3_ALERT_UNSUPPORTED_CERTIFICATE
                preverify_ok = false;
            }
 
            // verify X509 extended key usage
            if (self->x509_cert_eku_defined() && !self->verify_x509_cert_eku(current_cert))
            {
                OVPN_LOG_INFO("VERIFY FAIL -- bad X509 extended key usage in leaf certificate");
                if (self_ssl->authcert)
                    self_ssl->authcert->add_fail(depth,
                                                 AuthCert::Fail::BAD_CERT_TYPE,
                                                 "bad X509 extended key usage in leaf certificate");
                X509_STORE_CTX_set_error(ctx, X509_V_ERR_INVALID_PURPOSE); // alert code: SSL_R_SSLV3_ALERT_UNSUPPORTED_CERTIFICATE
                preverify_ok = false;
            }
 
            // get the Common name
            std::string cn = OpenSSLPKI::x509_get_field(current_cert, NID_commonName);
 
            // early rejection of Common Name?
            if (self->config->cn_reject_handler)
            {
                try
                {
                    if (self->config->cn_reject_handler->reject(cn))
                    {
                        OVPN_LOG_INFO("VERIFY FAIL -- early rejection of leaf cert Common Name");
                        X509_STORE_CTX_set_error(ctx, X509_V_ERR_CERT_REJECTED); // alert code: SSL_R_SSLV3_ALERT_BAD_CERTIFICATE
                        preverify_ok = false;
                    }
                }
                catch (const std::exception &e)
                {
                    OVPN_LOG_INFO("VERIFY FAIL -- early rejection of leaf cert Common Name due to handler exception: " << e.what());
                    X509_STORE_CTX_set_error(ctx, X509_V_ERR_CERT_REJECTED); // alert code: SSL_R_SSLV3_ALERT_BAD_CERTIFICATE
                    preverify_ok = false;
                }
            }
 
            if (self_ssl->authcert)
            {
                // save the Common Name
                self_ssl->authcert->cn = std::move(cn); // NOTE: cn is consumed!
 
                // save the leaf cert serial number
                load_serial_number_into_authcert(*self_ssl->authcert, current_cert);
 
                self_ssl->authcert->defined_ = true;
            }
        }
 
        // x509-track enabled?
        if (self_ssl->authcert && self_ssl->authcert->x509_track)
            x509_track_extract_from_cert(current_cert,
                                         depth,
                                         self->config->x509_track_config,
                                         *self_ssl->authcert->x509_track);
 
        return preverify_ok || self->deferred_cert_verify_failsafe(*self_ssl);
    }
 
    // Print debugging information on SSL/TLS session negotiation.
    static void info_callback(const ::SSL *s, int where, int ret)
    {
        if (where & SSL_CB_LOOP)
        {
            OVPN_LOG_INFO("SSL state ("
                          << ((where & SSL_ST_CONNECT)
                                  ? "connect"
                                  : (where & SSL_ST_ACCEPT
                                         ? "accept"
                                         : "undefined"))
                          << "): " << SSL_state_string_long(s));
        }
        if (where & SSL_CB_ALERT)
        {
            OVPN_LOG_INFO("SSL alert ("
                          << (where & SSL_CB_READ ? "read" : "write") << "): "
                          << SSL_alert_type_string_long(ret) << ": "
                          << SSL_alert_desc_string_long(ret));
        }
    }
 
    static int tls_ticket_key_callback(::SSL *ssl,
                                       unsigned char key_name[16],
                                       unsigned char iv[EVP_MAX_IV_LENGTH],
                                       ::EVP_CIPHER_CTX *ctx,
                                       ssl_mac_ctx *hctx,
                                       int enc)
    {
        // get OpenSSLContext
        const OpenSSLContext *self = (OpenSSLContext *)SSL_get_ex_data(ssl, SSL::context_data_index);
        if (!self)
            return -1;
 
        // get user-defined session ticket handler
        TLSSessionTicketBase *t = self->config->session_ticket_handler;
        if (!t)
            return -1;
 
        if (enc)
        {
            // create new ticket
            TLSSessionTicketBase::Name name;
            TLSSessionTicketBase::Key key;
 
            switch (t->create_session_ticket_key(name, key))
            {
            case TLSSessionTicketBase::NO_TICKET:
            case TLSSessionTicketBase::TICKET_EXPIRING: // doesn't really make sense for enc==1?
                return 0;
            case TLSSessionTicketBase::TICKET_AVAILABLE:
                if (!RAND_bytes(iv, EVP_MAX_IV_LENGTH))
                    return -1;
                if (!tls_ticket_init_cipher_hmac(key, iv, ctx, hctx, enc))
                    return -1;
                static_assert(TLSSessionTicketBase::Name::SIZE == 16, "unexpected name size");
                std::memcpy(key_name, name.value_, TLSSessionTicketBase::Name::SIZE);
                // OPENVPN_LOG("tls_ticket_key_callback: created ticket");
                return 1;
            default:
                // OPENVPN_LOG("tls_ticket_key_callback: create: bad ticket");
                return -1;
            }
        }
        else
        {
            // lookup existing ticket
            static_assert(TLSSessionTicketBase::Name::SIZE == 16, "unexpected name size");
            const TLSSessionTicketBase::Name name(key_name);
            TLSSessionTicketBase::Key key;
 
            switch (t->lookup_session_ticket_key(name, key))
            {
            case TLSSessionTicketBase::TICKET_AVAILABLE:
                if (!tls_ticket_init_cipher_hmac(key, iv, ctx, hctx, enc))
                    return -1;
                // OPENVPN_LOG("tls_ticket_key_callback: found ticket");
                return 1;
            case TLSSessionTicketBase::TICKET_EXPIRING:
                if (!tls_ticket_init_cipher_hmac(key, iv, ctx, hctx, enc))
                    return -1;
                // OPENVPN_LOG("tls_ticket_key_callback: expiring ticket");
                return 2;
            case TLSSessionTicketBase::NO_TICKET:
                // OPENVPN_LOG("tls_ticket_key_callback: lookup: no ticket");
                return 0;
            default:
                // OPENVPN_LOG("tls_ticket_key_callback: lookup: bad ticket");
                return -1;
            }
        }
    }
 
    static bool tls_ticket_init_cipher_hmac(const TLSSessionTicketBase::Key &key,
                                            unsigned char iv[EVP_MAX_IV_LENGTH],
                                            ::EVP_CIPHER_CTX *ctx,
                                            ssl_mac_ctx *mctx,
                                            const int enc)
    {
        static_assert(TLSSessionTicketBase::Key::CIPHER_KEY_SIZE == 32, "unexpected cipher key size");
        if (!EVP_CipherInit_ex(ctx, EVP_aes_256_cbc(), nullptr, key.cipher_value_, iv, enc))
            return false;
#if OPENSSL_VERSION_NUMBER >= 0x30000000L
        OSSL_PARAM params[]{
 
            /* The OSSL_PARAM_construct_utf8_string needs a non const str */
            OSSL_PARAM_construct_utf8_string("digest", (char *)"sha256", 0),
            OSSL_PARAM_construct_end()};
 
        if (!EVP_MAC_init(mctx, key.hmac_value_, TLSSessionTicketBase::Key::HMAC_KEY_SIZE, params))
            return false;
#else
        if (!HMAC_Init_ex(mctx, key.hmac_value_, TLSSessionTicketBase::Key::HMAC_KEY_SIZE, EVP_sha256(), nullptr))
            return false;
#endif
        return true;
    }
 
    static bool randomize_name_key(TLSSessionTicketBase::Name &name,
                                   TLSSessionTicketBase::Key &key)
    {
        if (!RAND_bytes(name.value_, TLSSessionTicketBase::Name::SIZE))
            return false;
        if (!RAND_bytes(key.cipher_value_, TLSSessionTicketBase::Key::CIPHER_KEY_SIZE))
            return false;
        if (!RAND_bytes(key.hmac_value_, TLSSessionTicketBase::Key::HMAC_KEY_SIZE))
            return false;
        return true;
    }
 
    static int client_hello_callback(::SSL *s, int *al, void *)
    {
        std::string sni_name;
 
        // get OpenSSLContext
        OpenSSLContext *self = (OpenSSLContext *)SSL_get_ex_data(s, SSL::context_data_index);
 
        // get OpenSSLContext::SSL
        SSL *self_ssl = (SSL *)SSL_get_ex_data(s, SSL::ssl_data_index);
 
        try
        {
            // get the SNI from the client hello
            sni_name = client_hello_get_sni(s);
 
            // process the SNI name, if provided
            if (!sni_name.empty())
            {
                // save the SNI name in authcert
                if (self_ssl->authcert)
                    self_ssl->authcert->sni = sni_name;
 
                // ignore the SNI if no handler was provided
                if (self->config->sni_handler)
                {
                    // get an alternative SSLFactoryAPI from the sni_handler
                    SSLFactoryAPI::Ptr fapi;
                    try
                    {
                        SNI::Metadata::UPtr sm;
                        fapi = self->config->sni_handler->sni_hello(sni_name, sm, self->config);
                        if (self_ssl->authcert)
                            self_ssl->authcert->sni_metadata = std::move(sm);
                    }
                    catch (const std::exception &e)
                    {
                        OPENVPN_LOG("SNI HANDLER ERROR: " << e.what());
                        return sni_error(e.what(), SSL_AD_INTERNAL_ERROR, self, self_ssl, al);
                    }
                    if (!fapi)
                        return sni_error("SNI name not found", SSL_AD_UNRECOGNIZED_NAME, self, self_ssl, al);
 
                    // make sure that returned SSLFactoryAPI is an OpenSSLContext
                    self_ssl->sni_ctx = fapi.dynamic_pointer_cast<OpenSSLContext>();
                    if (!self_ssl->sni_ctx)
                        throw Exception("sni_handler returned wrong kind of SSLFactoryAPI");
 
                    // don't modify SSL CTX if the returned SSLFactoryAPI is ourself
                    if (fapi.get() != self)
                    {
                        SSL_set_SSL_CTX(s, self_ssl->sni_ctx->ctx.get());
                        self_ssl->set_parent(self_ssl->sni_ctx.get());
                    }
                }
            }
            return SSL_CLIENT_HELLO_SUCCESS;
        }
        catch (const std::exception &e)
        {
            OPENVPN_LOG("SNI exception in OpenSSLContext, SNI=" << sni_name << " : " << e.what());
            *al = SSL_AD_INTERNAL_ERROR;
            return SSL_CLIENT_HELLO_ERROR;
        }
    }
 
    static int sni_error(std::string err,
                         const int ssl_ad_error,
                         OpenSSLContext *self,
                         SSL *self_ssl,
                         int *al)
    {
        if (self_ssl->authcert)
            self_ssl->authcert->add_fail(0, AuthCert::Fail::SNI_ERROR, std::move(err));
        if (self->deferred_cert_verify_failsafe(*self_ssl))
            return SSL_CLIENT_HELLO_SUCCESS;
        *al = ssl_ad_error;
        return SSL_CLIENT_HELLO_ERROR;
    }
 
    static size_t sni_get_len(ConstBuffer &buf)
    {
        size_t ret = buf.pop_front() << 8;
        ret += buf.pop_front();
        return ret;
    }
 
    static std::string client_hello_get_sni(::SSL *s)
    {
        const unsigned char *p;
        size_t remaining;
        if (!SSL_client_hello_get0_ext(s, TLSEXT_TYPE_server_name, &p, &remaining))
            return std::string();
 
        // For safety, map a ConstBuffer onto returned OpenSSL TLSEXT_TYPE_server_name data.
        ConstBuffer buf(p, remaining, true);
 
        // Extract the length of the supplied list of names,
        // and check that it matches size of remaining data
        // in buf.
        {
            const size_t len = sni_get_len(buf);
            if (len != buf.size())
                throw Exception("bad name list size");
        }
 
        // Next byte must be TLSEXT_NAMETYPE_host_name.
        if (buf.pop_front() != TLSEXT_NAMETYPE_host_name)
            throw Exception("expecting TLSEXT_NAMETYPE_host_name");
 
        // Now try to extract the SNI name.
        {
            const size_t len = sni_get_len(buf);
            if (len > buf.size())
                throw Exception("bad name size");
            if (!Unicode::is_valid_utf8_uchar_buf(buf.c_data(), len, 1024 | Unicode::UTF8_NO_CTRL))
                throw Exception("invalid UTF-8");
            return std::string((const char *)buf.c_data(), len);
        }
    }
 
    // Return true if we should continue with authentication
    // even though there was an error, because the user has
    // enabled SSLConst::DEFERRED_CERT_VERIFY and wants the
    // error to be logged in authcert so that it can be handled
    // by a higher layer.
    bool deferred_cert_verify_failsafe(const SSL &ssl) const
    {
        return (config->flags & SSLConst::DEFERRED_CERT_VERIFY)
               && ssl.authcert             // failsafe: don't defer error unless
               && ssl.authcert->is_fail(); //   authcert has recorded it
    }
 
    /* The order of epki and config is important here. epki holds a library
     * context that is need for the certificate (cert) object from config
     * with external key as that internally refrences the library context
     * and must not be destructed before the objects referencing it have
     * been destructed */
    std::shared_ptr<ExternalPKIImpl> epki = nullptr;
    Config::Ptr config;
 
    SSL_CTX_unique_ptr ctx{nullptr, &SSL_CTX_free};
    OpenSSLSessionCache::Ptr sess_cache; // client-side only
};
 
inline const std::string get_ssl_library_version()
{
    return OpenSSL_version(OPENSSL_VERSION);
}
} // namespace openvpn
#endif