@deftypefun {void} {gnutls_psk_set_server_credentials_function} (gnutls_psk_server_credentials_t         @var{cred}, gnutls_psk_server_credentials_function         * @var{func})

@var{cred}: is a @code{gnutls_psk_server_credentials_t}  type.

@var{func}: is the callback function

This function can be used to set a callback to retrieve the user's PSK credentials.

The callback's function form is:

int (*callback)(gnutls_session_t, const char* username,

gnutls_datum_t* key);

 @code{username} contains the actual username.

The  @code{key} must be filled in using the @code{gnutls_malloc()} .

In case the callback returned a negative number then gnutls will

assume that the username does not exist.

The callback function will only be called once per handshake.  The

callback function should return 0 on success, while -1 indicates

an error.

@end deftypefun