naiveproxy/net/socket/ssl_server_socket_impl.cc

// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/socket/ssl_server_socket_impl.h"

#include <utility>

#include "base/callback_helpers.h"
#include "base/logging.h"
#include "base/strings/string_util.h"
#include "crypto/openssl_util.h"
#include "crypto/rsa_private_key.h"
#include "net/base/net_errors.h"
#include "net/cert/cert_verify_result.h"
#include "net/cert/client_cert_verifier.h"
#include "net/cert/x509_util.h"
#include "net/log/net_log_event_type.h"
#include "net/log/net_log_with_source.h"
#include "net/socket/socket_bio_adapter.h"
#include "net/ssl/openssl_ssl_util.h"
#include "net/ssl/ssl_connection_status_flags.h"
#include "net/ssl/ssl_info.h"
#include "third_party/boringssl/src/include/openssl/err.h"
#include "third_party/boringssl/src/include/openssl/pool.h"
#include "third_party/boringssl/src/include/openssl/ssl.h"

#define GotoState(s) next_handshake_state_ = s

namespace net {

class SSLServerContextImpl::SocketImpl : public SSLServerSocket,
                                         public SocketBIOAdapter::Delegate {
 public:
  SocketImpl(SSLServerContextImpl* context,
             std::unique_ptr<StreamSocket> socket);
  ~SocketImpl() override;

  // SSLServerSocket interface.
  int Handshake(const CompletionCallback& callback) override;

  // SSLSocket interface.
  int ExportKeyingMaterial(const base::StringPiece& label,
                           bool has_context,
                           const base::StringPiece& context,
                           unsigned char* out,
                           unsigned int outlen) override;

  // Socket interface (via StreamSocket).
  int Read(IOBuffer* buf,
           int buf_len,
           const CompletionCallback& callback) override;
  int Write(IOBuffer* buf,
            int buf_len,
            const CompletionCallback& callback) override;
  int SetReceiveBufferSize(int32_t size) override;
  int SetSendBufferSize(int32_t size) override;

  // StreamSocket implementation.
  int Connect(const CompletionCallback& callback) override;
  void Disconnect() override;
  bool IsConnected() const override;
  bool IsConnectedAndIdle() const override;
  int GetPeerAddress(IPEndPoint* address) const override;
  int GetLocalAddress(IPEndPoint* address) const override;
  const NetLogWithSource& NetLog() const override;
  void SetSubresourceSpeculation() override;
  void SetOmniboxSpeculation() override;
  bool WasEverUsed() const override;
  bool WasAlpnNegotiated() const override;
  NextProto GetNegotiatedProtocol() const override;
  bool GetSSLInfo(SSLInfo* ssl_info) override;
  void GetConnectionAttempts(ConnectionAttempts* out) const override;
  void ClearConnectionAttempts() override {}
  void AddConnectionAttempts(const ConnectionAttempts& attempts) override {}
  int64_t GetTotalReceivedBytes() const override;
  static ssl_verify_result_t CertVerifyCallback(SSL* ssl, uint8_t* out_alert);
  ssl_verify_result_t CertVerifyCallbackImpl(uint8_t* out_alert);

  // SocketBIOAdapter::Delegate implementation.
  void OnReadReady() override;
  void OnWriteReady() override;

 private:
  enum State {
    STATE_NONE,
    STATE_HANDSHAKE,
  };

  void OnHandshakeIOComplete(int result);

  int DoPayloadRead();
  int DoPayloadWrite();

  int DoHandshakeLoop(int last_io_result);
  int DoHandshake();
  void DoHandshakeCallback(int result);
  void DoReadCallback(int result);
  void DoWriteCallback(int result);

  int Init();
  void ExtractClientCert();

  SSLServerContextImpl* context_;

  NetLogWithSource net_log_;

  CompletionCallback user_handshake_callback_;
  CompletionCallback user_read_callback_;
  CompletionCallback user_write_callback_;

  // Used by Read function.
  scoped_refptr<IOBuffer> user_read_buf_;
  int user_read_buf_len_;

  // Used by Write function.
  scoped_refptr<IOBuffer> user_write_buf_;
  int user_write_buf_len_;

  // OpenSSL stuff
  bssl::UniquePtr<SSL> ssl_;

  // StreamSocket for sending and receiving data.
  std::unique_ptr<StreamSocket> transport_socket_;
  std::unique_ptr<SocketBIOAdapter> transport_adapter_;

  // Certificate for the client.
  scoped_refptr<X509Certificate> client_cert_;

  State next_handshake_state_;
  bool completed_handshake_;

  DISALLOW_COPY_AND_ASSIGN(SocketImpl);
};

SSLServerContextImpl::SocketImpl::SocketImpl(
    SSLServerContextImpl* context,
    std::unique_ptr<StreamSocket> transport_socket)
    : context_(context),
      user_read_buf_len_(0),
      user_write_buf_len_(0),
      transport_socket_(std::move(transport_socket)),
      next_handshake_state_(STATE_NONE),
      completed_handshake_(false) {
  ssl_.reset(SSL_new(context_->ssl_ctx_.get()));
  SSL_set_app_data(ssl_.get(), this);
}

SSLServerContextImpl::SocketImpl::~SocketImpl() {
  if (ssl_) {
    // Calling SSL_shutdown prevents the session from being marked as
    // unresumable.
    SSL_shutdown(ssl_.get());
    ssl_.reset();
  }
}

int SSLServerContextImpl::SocketImpl::Handshake(
    const CompletionCallback& callback) {
  net_log_.BeginEvent(NetLogEventType::SSL_SERVER_HANDSHAKE);

  // Set up new ssl object.
  int rv = Init();
  if (rv != OK) {
    LOG(ERROR) << "Failed to initialize OpenSSL: rv=" << rv;
    net_log_.EndEventWithNetErrorCode(NetLogEventType::SSL_SERVER_HANDSHAKE,
                                      rv);
    return rv;
  }

  // Set SSL to server mode. Handshake happens in the loop below.
  SSL_set_accept_state(ssl_.get());

  GotoState(STATE_HANDSHAKE);
  rv = DoHandshakeLoop(OK);
  if (rv == ERR_IO_PENDING) {
    user_handshake_callback_ = callback;
  } else {
    net_log_.EndEventWithNetErrorCode(NetLogEventType::SSL_SERVER_HANDSHAKE,
                                      rv);
  }

  return rv > OK ? OK : rv;
}

int SSLServerContextImpl::SocketImpl::ExportKeyingMaterial(
    const base::StringPiece& label,
    bool has_context,
    const base::StringPiece& context,
    unsigned char* out,
    unsigned int outlen) {
  if (!IsConnected())
    return ERR_SOCKET_NOT_CONNECTED;

  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);

  int rv = SSL_export_keying_material(
      ssl_.get(), out, outlen, label.data(), label.size(),
      reinterpret_cast<const unsigned char*>(context.data()), context.length(),
      context.length() > 0);

  if (rv != 1) {
    int ssl_error = SSL_get_error(ssl_.get(), rv);
    LOG(ERROR) << "Failed to export keying material;"
               << " returned " << rv << ", SSL error code " << ssl_error;
    return MapOpenSSLError(ssl_error, err_tracer);
  }
  return OK;
}

int SSLServerContextImpl::SocketImpl::Read(IOBuffer* buf,
                                           int buf_len,
                                           const CompletionCallback& callback) {
  DCHECK(user_read_callback_.is_null());
  DCHECK(user_handshake_callback_.is_null());
  DCHECK(!user_read_buf_);
  DCHECK(!callback.is_null());

  user_read_buf_ = buf;
  user_read_buf_len_ = buf_len;

  DCHECK(completed_handshake_);

  int rv = DoPayloadRead();

  if (rv == ERR_IO_PENDING) {
    user_read_callback_ = callback;
  } else {
    user_read_buf_ = NULL;
    user_read_buf_len_ = 0;
  }

  return rv;
}

int SSLServerContextImpl::SocketImpl::Write(
    IOBuffer* buf,
    int buf_len,
    const CompletionCallback& callback) {
  DCHECK(user_write_callback_.is_null());
  DCHECK(!user_write_buf_);
  DCHECK(!callback.is_null());

  user_write_buf_ = buf;
  user_write_buf_len_ = buf_len;

  int rv = DoPayloadWrite();

  if (rv == ERR_IO_PENDING) {
    user_write_callback_ = callback;
  } else {
    user_write_buf_ = NULL;
    user_write_buf_len_ = 0;
  }
  return rv;
}

int SSLServerContextImpl::SocketImpl::SetReceiveBufferSize(int32_t size) {
  return transport_socket_->SetReceiveBufferSize(size);
}

int SSLServerContextImpl::SocketImpl::SetSendBufferSize(int32_t size) {
  return transport_socket_->SetSendBufferSize(size);
}

int SSLServerContextImpl::SocketImpl::Connect(
    const CompletionCallback& callback) {
  NOTIMPLEMENTED();
  return ERR_NOT_IMPLEMENTED;
}

void SSLServerContextImpl::SocketImpl::Disconnect() {
  transport_socket_->Disconnect();
}

bool SSLServerContextImpl::SocketImpl::IsConnected() const {
  // TODO(wtc): Find out if we should check transport_socket_->IsConnected()
  // as well.
  return completed_handshake_;
}

bool SSLServerContextImpl::SocketImpl::IsConnectedAndIdle() const {
  return completed_handshake_ && transport_socket_->IsConnectedAndIdle();
}

int SSLServerContextImpl::SocketImpl::GetPeerAddress(
    IPEndPoint* address) const {
  if (!IsConnected())
    return ERR_SOCKET_NOT_CONNECTED;
  return transport_socket_->GetPeerAddress(address);
}

int SSLServerContextImpl::SocketImpl::GetLocalAddress(
    IPEndPoint* address) const {
  if (!IsConnected())
    return ERR_SOCKET_NOT_CONNECTED;
  return transport_socket_->GetLocalAddress(address);
}

const NetLogWithSource& SSLServerContextImpl::SocketImpl::NetLog() const {
  return net_log_;
}

void SSLServerContextImpl::SocketImpl::SetSubresourceSpeculation() {
  transport_socket_->SetSubresourceSpeculation();
}

void SSLServerContextImpl::SocketImpl::SetOmniboxSpeculation() {
  transport_socket_->SetOmniboxSpeculation();
}

bool SSLServerContextImpl::SocketImpl::WasEverUsed() const {
  return transport_socket_->WasEverUsed();
}

bool SSLServerContextImpl::SocketImpl::WasAlpnNegotiated() const {
  NOTIMPLEMENTED();
  return false;
}

NextProto SSLServerContextImpl::SocketImpl::GetNegotiatedProtocol() const {
  // ALPN is not supported by this class.
  return kProtoUnknown;
}

bool SSLServerContextImpl::SocketImpl::GetSSLInfo(SSLInfo* ssl_info) {
  ssl_info->Reset();
  if (!completed_handshake_)
    return false;

  ssl_info->cert = client_cert_;

  const SSL_CIPHER* cipher = SSL_get_current_cipher(ssl_.get());
  CHECK(cipher);
  ssl_info->security_bits = SSL_CIPHER_get_bits(cipher, NULL);

  SSLConnectionStatusSetCipherSuite(
      static_cast<uint16_t>(SSL_CIPHER_get_id(cipher)),
      &ssl_info->connection_status);
  SSLConnectionStatusSetVersion(GetNetSSLVersion(ssl_.get()),
                                &ssl_info->connection_status);

  ssl_info->handshake_type = SSL_session_reused(ssl_.get())
                                 ? SSLInfo::HANDSHAKE_RESUME
                                 : SSLInfo::HANDSHAKE_FULL;

  return true;
}

void SSLServerContextImpl::SocketImpl::GetConnectionAttempts(
    ConnectionAttempts* out) const {
  out->clear();
}

int64_t SSLServerContextImpl::SocketImpl::GetTotalReceivedBytes() const {
  return transport_socket_->GetTotalReceivedBytes();
}

void SSLServerContextImpl::SocketImpl::OnReadReady() {
  if (next_handshake_state_ == STATE_HANDSHAKE) {
    // In handshake phase. The parameter to OnHandshakeIOComplete is unused.
    OnHandshakeIOComplete(OK);
    return;
  }

  // BoringSSL does not support renegotiation as a server, so the only other
  // operation blocked on Read is DoPayloadRead.
  if (!user_read_buf_)
    return;

  int rv = DoPayloadRead();
  if (rv != ERR_IO_PENDING)
    DoReadCallback(rv);
}

void SSLServerContextImpl::SocketImpl::OnWriteReady() {
  if (next_handshake_state_ == STATE_HANDSHAKE) {
    // In handshake phase. The parameter to OnHandshakeIOComplete is unused.
    OnHandshakeIOComplete(OK);
    return;
  }

  // BoringSSL does not support renegotiation as a server, so the only other
  // operation blocked on Read is DoPayloadWrite.
  if (!user_write_buf_)
    return;

  int rv = DoPayloadWrite();
  if (rv != ERR_IO_PENDING)
    DoWriteCallback(rv);
}

void SSLServerContextImpl::SocketImpl::OnHandshakeIOComplete(int result) {
  int rv = DoHandshakeLoop(result);
  if (rv == ERR_IO_PENDING)
    return;

  net_log_.EndEventWithNetErrorCode(NetLogEventType::SSL_SERVER_HANDSHAKE, rv);
  if (!user_handshake_callback_.is_null())
    DoHandshakeCallback(rv);
}

int SSLServerContextImpl::SocketImpl::DoPayloadRead() {
  DCHECK(completed_handshake_);
  DCHECK_EQ(STATE_NONE, next_handshake_state_);
  DCHECK(user_read_buf_);
  DCHECK_GT(user_read_buf_len_, 0);

  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
  int rv = SSL_read(ssl_.get(), user_read_buf_->data(), user_read_buf_len_);
  if (rv >= 0)
    return rv;
  int ssl_error = SSL_get_error(ssl_.get(), rv);
  OpenSSLErrorInfo error_info;
  int net_error =
      MapOpenSSLErrorWithDetails(ssl_error, err_tracer, &error_info);
  if (net_error != ERR_IO_PENDING) {
    net_log_.AddEvent(
        NetLogEventType::SSL_READ_ERROR,
        CreateNetLogOpenSSLErrorCallback(net_error, ssl_error, error_info));
  }
  return net_error;
}

int SSLServerContextImpl::SocketImpl::DoPayloadWrite() {
  DCHECK(completed_handshake_);
  DCHECK_EQ(STATE_NONE, next_handshake_state_);
  DCHECK(user_write_buf_);

  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
  int rv = SSL_write(ssl_.get(), user_write_buf_->data(), user_write_buf_len_);
  if (rv >= 0)
    return rv;
  int ssl_error = SSL_get_error(ssl_.get(), rv);
  OpenSSLErrorInfo error_info;
  int net_error =
      MapOpenSSLErrorWithDetails(ssl_error, err_tracer, &error_info);
  if (net_error != ERR_IO_PENDING) {
    net_log_.AddEvent(
        NetLogEventType::SSL_WRITE_ERROR,
        CreateNetLogOpenSSLErrorCallback(net_error, ssl_error, error_info));
  }
  return net_error;
}

int SSLServerContextImpl::SocketImpl::DoHandshakeLoop(int last_io_result) {
  int rv = last_io_result;
  do {
    // Default to STATE_NONE for next state.
    // (This is a quirk carried over from the windows
    // implementation.  It makes reading the logs a bit harder.)
    // State handlers can and often do call GotoState just
    // to stay in the current state.
    State state = next_handshake_state_;
    GotoState(STATE_NONE);
    switch (state) {
      case STATE_HANDSHAKE:
        rv = DoHandshake();
        break;
      case STATE_NONE:
      default:
        rv = ERR_UNEXPECTED;
        LOG(DFATAL) << "unexpected state " << state;
        break;
    }
  } while (rv != ERR_IO_PENDING && next_handshake_state_ != STATE_NONE);
  return rv;
}

int SSLServerContextImpl::SocketImpl::DoHandshake() {
  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);
  int net_error = OK;
  int rv = SSL_do_handshake(ssl_.get());

  if (rv == 1) {
    completed_handshake_ = true;
    STACK_OF(CRYPTO_BUFFER)* certs = SSL_get0_peer_certificates(ssl_.get());
    if (certs) {
      client_cert_ = x509_util::CreateX509CertificateFromBuffers(certs);
      if (!client_cert_)
        return ERR_SSL_CLIENT_AUTH_CERT_BAD_FORMAT;
    }
  } else {
    int ssl_error = SSL_get_error(ssl_.get(), rv);
    OpenSSLErrorInfo error_info;
    net_error = MapOpenSSLErrorWithDetails(ssl_error, err_tracer, &error_info);

    // SSL_R_CERTIFICATE_VERIFY_FAILED's mapping is different between client and
    // server.
    if (ERR_GET_LIB(error_info.error_code) == ERR_LIB_SSL &&
        ERR_GET_REASON(error_info.error_code) ==
            SSL_R_CERTIFICATE_VERIFY_FAILED) {
      net_error = ERR_BAD_SSL_CLIENT_AUTH_CERT;
    }

    // If not done, stay in this state
    if (net_error == ERR_IO_PENDING) {
      GotoState(STATE_HANDSHAKE);
    } else {
      LOG(ERROR) << "handshake failed; returned " << rv << ", SSL error code "
                 << ssl_error << ", net_error " << net_error;
      net_log_.AddEvent(
          NetLogEventType::SSL_HANDSHAKE_ERROR,
          CreateNetLogOpenSSLErrorCallback(net_error, ssl_error, error_info));
    }
  }
  return net_error;
}

void SSLServerContextImpl::SocketImpl::DoHandshakeCallback(int rv) {
  DCHECK_NE(rv, ERR_IO_PENDING);
  base::ResetAndReturn(&user_handshake_callback_).Run(rv > OK ? OK : rv);
}

void SSLServerContextImpl::SocketImpl::DoReadCallback(int rv) {
  DCHECK(rv != ERR_IO_PENDING);
  DCHECK(!user_read_callback_.is_null());

  user_read_buf_ = NULL;
  user_read_buf_len_ = 0;
  base::ResetAndReturn(&user_read_callback_).Run(rv);
}

void SSLServerContextImpl::SocketImpl::DoWriteCallback(int rv) {
  DCHECK(rv != ERR_IO_PENDING);
  DCHECK(!user_write_callback_.is_null());

  user_write_buf_ = NULL;
  user_write_buf_len_ = 0;
  base::ResetAndReturn(&user_write_callback_).Run(rv);
}

int SSLServerContextImpl::SocketImpl::Init() {
  static const int kBufferSize = 17 * 1024;

  crypto::OpenSSLErrStackTracer err_tracer(FROM_HERE);

  if (!ssl_)
    return ERR_UNEXPECTED;

  // Set certificate and private key.
  DCHECK(context_->cert_->os_cert_handle());
  DCHECK(context_->key_->key());
  if (!SetSSLChainAndKey(ssl_.get(), context_->cert_.get(),
                         context_->key_->key(), nullptr)) {
    return ERR_UNEXPECTED;
  }

  transport_adapter_.reset(new SocketBIOAdapter(
      transport_socket_.get(), kBufferSize, kBufferSize, this));
  BIO* transport_bio = transport_adapter_->bio();

  BIO_up_ref(transport_bio);  // SSL_set0_rbio takes ownership.
  SSL_set0_rbio(ssl_.get(), transport_bio);

  BIO_up_ref(transport_bio);  // SSL_set0_wbio takes ownership.
  SSL_set0_wbio(ssl_.get(), transport_bio);

  return OK;
}

// static
ssl_verify_result_t SSLServerContextImpl::SocketImpl::CertVerifyCallback(
    SSL* ssl,
    uint8_t* out_alert) {
  SocketImpl* socket = reinterpret_cast<SocketImpl*>(SSL_get_app_data(ssl));
  return socket->CertVerifyCallbackImpl(out_alert);
}

ssl_verify_result_t SSLServerContextImpl::SocketImpl::CertVerifyCallbackImpl(
    uint8_t* out_alert) {
  ClientCertVerifier* verifier =
      context_->ssl_server_config_.client_cert_verifier;
  // If a verifier was not supplied, all certificates are accepted.
  if (!verifier)
    return ssl_verify_ok;

  scoped_refptr<X509Certificate> client_cert =
      x509_util::CreateX509CertificateFromBuffers(
          SSL_get0_peer_certificates(ssl_.get()));
  if (!client_cert) {
    *out_alert = SSL_AD_BAD_CERTIFICATE;
    return ssl_verify_invalid;
  }

  // TODO(davidben): Support asynchronous verifiers. http://crbug.com/347402
  std::unique_ptr<ClientCertVerifier::Request> ignore_async;
  int res =
      verifier->Verify(client_cert.get(), CompletionCallback(), &ignore_async);
  DCHECK_NE(res, ERR_IO_PENDING);

  if (res != OK) {
    // TODO(davidben): Map from certificate verification failure to alert.
    *out_alert = SSL_AD_CERTIFICATE_UNKNOWN;
    return ssl_verify_invalid;
  }
  return ssl_verify_ok;
}

std::unique_ptr<SSLServerContext> CreateSSLServerContext(
    X509Certificate* certificate,
    const crypto::RSAPrivateKey& key,
    const SSLServerConfig& ssl_server_config) {
  return std::unique_ptr<SSLServerContext>(
      new SSLServerContextImpl(certificate, key, ssl_server_config));
}

SSLServerContextImpl::SSLServerContextImpl(
    X509Certificate* certificate,
    const crypto::RSAPrivateKey& key,
    const SSLServerConfig& ssl_server_config)
    : ssl_server_config_(ssl_server_config),
      cert_(certificate),
      key_(key.Copy()) {
  CHECK(key_);
  crypto::EnsureOpenSSLInit();
  ssl_ctx_.reset(SSL_CTX_new(TLS_with_buffers_method()));
  SSL_CTX_set_session_cache_mode(ssl_ctx_.get(), SSL_SESS_CACHE_SERVER);
  uint8_t session_ctx_id = 0;
  SSL_CTX_set_session_id_context(ssl_ctx_.get(), &session_ctx_id,
                                 sizeof(session_ctx_id));
  // Deduplicate all certificates minted from the SSL_CTX in memory.
  SSL_CTX_set0_buffer_pool(ssl_ctx_.get(), x509_util::GetBufferPool());

  int verify_mode = 0;
  switch (ssl_server_config_.client_cert_type) {
    case SSLServerConfig::ClientCertType::REQUIRE_CLIENT_CERT:
      verify_mode |= SSL_VERIFY_FAIL_IF_NO_PEER_CERT;
    // Fall-through
    case SSLServerConfig::ClientCertType::OPTIONAL_CLIENT_CERT:
      verify_mode |= SSL_VERIFY_PEER;
      SSL_CTX_set_custom_verify(ssl_ctx_.get(), verify_mode,
                                SocketImpl::CertVerifyCallback);
      break;
    case SSLServerConfig::ClientCertType::NO_CLIENT_CERT:
      break;
  }

  DCHECK_LT(SSL3_VERSION, ssl_server_config_.version_min);
  DCHECK_LT(SSL3_VERSION, ssl_server_config_.version_max);
  CHECK(SSL_CTX_set_min_proto_version(ssl_ctx_.get(),
                                      ssl_server_config_.version_min));
  CHECK(SSL_CTX_set_max_proto_version(ssl_ctx_.get(),
                                      ssl_server_config_.version_max));

  // OpenSSL defaults some options to on, others to off. To avoid ambiguity,
  // set everything we care about to an absolute value.
  SslSetClearMask options;
  options.ConfigureFlag(SSL_OP_NO_COMPRESSION, true);

  SSL_CTX_set_options(ssl_ctx_.get(), options.set_mask);
  SSL_CTX_clear_options(ssl_ctx_.get(), options.clear_mask);

  // Same as above, this time for the SSL mode.
  SslSetClearMask mode;

  mode.ConfigureFlag(SSL_MODE_RELEASE_BUFFERS, true);

  SSL_CTX_set_mode(ssl_ctx_.get(), mode.set_mask);
  SSL_CTX_clear_mode(ssl_ctx_.get(), mode.clear_mask);

  // See SSLServerConfig::disabled_cipher_suites for description of the suites
  // disabled by default. Note that !SHA256 and !SHA384 only remove HMAC-SHA256
  // and HMAC-SHA384 cipher suites, not GCM cipher suites with SHA256 or SHA384
  // as the handshake hash.
  std::string command("DEFAULT:!SHA256:!SHA384:!AESGCM+AES256:!aPSK");

  if (ssl_server_config_.require_ecdhe)
    command.append(":!kRSA");

  // Remove any disabled ciphers.
  for (uint16_t id : ssl_server_config_.disabled_cipher_suites) {
    const SSL_CIPHER* cipher = SSL_get_cipher_by_value(id);
    if (cipher) {
      command.append(":!");
      command.append(SSL_CIPHER_get_name(cipher));
    }
  }

  CHECK(SSL_CTX_set_strict_cipher_list(ssl_ctx_.get(), command.c_str()));

  if (ssl_server_config_.client_cert_type !=
          SSLServerConfig::ClientCertType::NO_CLIENT_CERT &&
      !ssl_server_config_.cert_authorities_.empty()) {
    bssl::UniquePtr<STACK_OF(CRYPTO_BUFFER)> stack(sk_CRYPTO_BUFFER_new_null());
    for (const auto& authority : ssl_server_config_.cert_authorities_) {
      sk_CRYPTO_BUFFER_push(stack.get(),
                            x509_util::CreateCryptoBuffer(authority).release());
    }
    SSL_CTX_set0_client_CAs(ssl_ctx_.get(), stack.release());
  }
}

SSLServerContextImpl::~SSLServerContextImpl() = default;

std::unique_ptr<SSLServerSocket> SSLServerContextImpl::CreateSSLServerSocket(
    std::unique_ptr<StreamSocket> socket) {
  return std::unique_ptr<SSLServerSocket>(
      new SocketImpl(this, std::move(socket)));
}

}  // namespace net