@deftypefun {int} {gnutls_x509_crt_get_subject_alt_name} (gnutls_x509_crt_t @var{cert}, unsigned int @var{seq}, void * @var{san}, size_t * @var{san_size}, unsigned int * @var{critical})
@var{cert}: should contain a @code{gnutls_x509_crt_t}  type

@var{seq}: specifies the sequence number of the alt name (0 for the first one, 1 for the second etc.)

@var{san}: is the place where the alternative name will be copied to

@var{san_size}: holds the size of san.

@var{critical}: will be non-zero if the extension is marked as critical (may be null)

This function retrieves the Alternative Name (2.5.29.17), contained
in the given certificate in the X509v3 Certificate Extensions.

When the SAN type is otherName, it will extract the data in the
otherName's value field, and @code{GNUTLS_SAN_OTHERNAME}  is returned.
You may use @code{gnutls_x509_crt_get_subject_alt_othername_oid()}  to get
the corresponding OID and the "virtual" SAN types (e.g.,
@code{GNUTLS_SAN_OTHERNAME_XMPP} ).

If an otherName OID is known, the data will be decoded.  Otherwise
the returned data will be DER encoded, and you will have to decode
it yourself.  Currently, only the RFC 3920 id-on-xmppAddr SAN is
recognized.

@strong{Returns:} the alternative subject name type on success, one of the
enumerated @code{gnutls_x509_subject_alt_name_t} .  It will return
@code{GNUTLS_E_SHORT_MEMORY_BUFFER}  if  @code{san_size} is not large enough to
hold the value.  In that case  @code{san_size} will be updated with the
required size.  If the certificate does not have an Alternative
name with the specified sequence number then
@code{GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE}  is returned.
@end deftypefun