SSL_CTX_add_extra_chain_cert, SSL_CTX_clear_extra_chain_certs - add or clear
  extra chain certificates
 #include <openssl/ssl.h>
 long SSL_CTX_add_extra_chain_cert(SSL_CTX *ctx, X509 *x509);
 long SSL_CTX_clear_extra_chain_certs(SSL_CTX *ctx);
SSL_CTX_add_extra_chain_cert() adds the certificate x509 to the
  extra chain certificates associated with ctx. Several certificates can
  be added one after another.
SSL_CTX_clear_extra_chain_certs() clears all extra chain
    certificates associated with ctx.
These functions are implemented as macros.
When sending a certificate chain, extra chain certificates are sent in order
  following the end entity certificate.
If no chain is specified, the library will try to complete the
    chain from the available CA certificates in the trusted CA storage, see
    SSL_CTX_load_verify_locations(3).
The x509 certificate provided to
    SSL_CTX_add_extra_chain_cert() will be freed by the library when the
    SSL_CTX is destroyed. An application should not free the
    x509 object.
Only one set of extra chain certificates can be specified per SSL_CTX structure.
  Different chains for different certificates (for example if both RSA and DSA
  certificates are specified by the same server) or different SSL structures
  with the same parent SSL_CTX cannot be specified using this function. For more
  flexibility functions such as SSL_add1_chain_cert() should be used
  instead.
SSL_CTX_add_extra_chain_cert() and
  SSL_CTX_clear_extra_chain_certs() return 1 on success and 0 for
  failure. Check out the error stack to find out the reason for failure.
ssl(7), SSL_CTX_use_certificate(3),
  SSL_CTX_set_client_cert_cb(3), SSL_CTX_load_verify_locations(3)
  SSL_CTX_set0_chain(3) SSL_CTX_set1_chain(3)
  SSL_CTX_add0_chain_cert(3) SSL_CTX_add1_chain_cert(3)
  SSL_set0_chain(3) SSL_set1_chain(3)
  SSL_add0_chain_cert(3) SSL_add1_chain_cert(3)
  SSL_CTX_build_cert_chain(3) SSL_build_cert_chain(3)
Copyright 2000-2016 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>.