@deftypefun {int} {gnutls_certificate_set_x509_key_file} (gnutls_certificate_credentials_t @var{res}, const char * @var{certfile}, const char * @var{keyfile}, gnutls_x509_crt_fmt_t @var{type})
@var{res}: is a @code{gnutls_certificate_credentials_t}  type.

@var{certfile}: is a file that containing the certificate list (path) for
the specified private key, in PKCS7 format, or a list of certificates

@var{keyfile}: is a file that contains the private key

@var{type}: is PEM or DER

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 need to send more than its own end
entity certificate, e.g., also an intermediate CA cert, then the
 @code{certfile} must contain the ordered certificate chain.

Note that the names in the certificate provided will be considered
when selecting the appropriate certificate to use (in case of multiple
certificate/key pairs).

This function can also accept URLs at  @code{keyfile} and  @code{certfile} . In that case it
will use the private key and certificate indicated by the URLs. Note
that the supported URLs are the ones indicated by @code{gnutls_url_is_supported()} .

In case the  @code{certfile} is provided as a PKCS @code{11}  URL, then the certificate, and its
present issuers in the token are imported (i.e., forming the required trust chain).

If that function fails to load the  @code{res} structure 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:} 3.1.11
@end deftypefun