@deftypefun {int} {gnutls_psk_set_client_credentials} (gnutls_psk_client_credentials_t @var{res}, const char * @var{username}, const gnutls_datum_t * @var{key}, gnutls_psk_key_flags @var{flags})
@var{res}: is a @code{gnutls_psk_client_credentials_t}  type.

@var{username}: is the user's zero-terminated userid

@var{key}: is the user's key

@var{flags}: indicate the format of the key, either
@code{GNUTLS_PSK_KEY_RAW}  or @code{GNUTLS_PSK_KEY_HEX} .

This function sets the username and password, in a
gnutls_psk_client_credentials_t type.  Those will be used in
PSK authentication.   @code{username} should be an ASCII string or UTF-8
string. In case of a UTF-8 string it is recommended to be following
the PRECIS framework for usernames (rfc8265). The key can be either
in raw byte format or in Hex format (without the 0x prefix).

@strong{Returns:} On success, @code{GNUTLS_E_SUCCESS}  (0) is returned, otherwise
an error code is returned.
@end deftypefun