@deftypefun {void} {gnutls_certificate_set_pin_function} (gnutls_certificate_credentials_t       @var{cred}, gnutls_pin_callback_t @var{fn}, void * @var{userdata})
@var{cred}: is a @code{gnutls_certificate_credentials_t}  type.

@var{fn}: A PIN callback

@var{userdata}: Data to be passed in the callback

This function will set a callback function to be used when
required to access a protected object. This function overrides any other
global PIN functions.

Note that this function must be called right after initialization
to have effect.

@strong{Since:} 3.1.0
@end deftypefun