@deftypefun {int} {gnutls_x509_crt_get_signature_oid} (gnutls_x509_crt_t @var{cert}, char * @var{oid}, size_t * @var{oid_size})

@var{cert}: should contain a @code{gnutls_x509_crt_t}  type

@var{oid}: a pointer to a buffer to hold the OID (may be null)

@var{oid_size}: initially holds the size of  @code{oid} 

This function will return the OID of the signature algorithm

that has been used to sign this certificate. This is function

is useful in the case @code{gnutls_x509_crt_get_signature_algorithm()} 

returned @code{GNUTLS_SIGN_UNKNOWN} .

@strong{Returns:} zero or a negative error code on error.

@strong{Since:} 3.5.0

@end deftypefun