@deftypefun {int} {gnutls_certificate_set_x509_key} (gnutls_certificate_credentials_t @var{res}, gnutls_x509_crt_t * @var{cert_list}, int @var{cert_list_size}, gnutls_x509_privkey_t @var{key})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{cert_list}: contains a certificate list (path) for the specified private key

@var{cert_list_size}: holds the size of the certificate list

@var{key}: is a @code{gnutls_x509_privkey_t}  key

This function sets a certificate/private key pair in the
gnutls_certificate_credentials_t type.  This function may be
called more than once, in case multiple keys/certificates exist for
the server.  For clients that wants to send more than their own end
entity certificate (e.g., also an intermediate CA cert) then put
the certificate chain in  @code{cert_list} .

Note that the certificates and keys provided, can be safely deinitialized
after this function is called.

If that function fails to load the  @code{res} type is at an undefined state, it must
not be reused to load other keys or certificates.

Note that, this function by default returns zero on success and a negative value on error.
Since 3.5.6, when the flag @code{GNUTLS_CERTIFICATE_API_V2}  is set using @code{gnutls_certificate_set_flags()} 
it returns an index (greater or equal to zero). That index can be used to other functions to refer to the added key-pair.

@strong{Returns:} On success this functions returns zero, and otherwise a negative value on error (see above for modifying that behavior).

@strong{Since:} 2.4.0
@end deftypefun