SSL_get_server_tmp_key - get information about the server's temporary key used
  during a handshake
 #include <openssl/ssl.h>
 long SSL_get_server_tmp_key(SSL *ssl, EVP_PKEY **key);
SSL_get_server_tmp_key() returns the temporary key provided by the server
  and used during key exchange. For example, if ECDHE is in use, then this
  represents the server's public ECDHE key. On success a pointer to the key is
  stored in *key. It is the caller's responsibility to free this key
  after use using EVP_PKEY_free(3). This function may only be called by
  the client.
SSL_get_server_tmp_key() returns 1 on success or 0 otherwise.
This function is implemented as a macro.
Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (the "License"). You
    may not use this file except in compliance with the License. You can obtain
    a copy in the file LICENSE in the source distribution or at
    <https://www.openssl.org/source/license.html>.