Specify the callback function to use in the client to chose a new
pin, possibly suggested by the server, for the SECURID mechanism.
This is not normally invoked, but only when the server requests it.
The function can be later retrieved using
This function is part of the old callback interface.
The new interface uses gsasl_callback_set() to set the application
callback, and uses gsasl_callback() or gsasl_property_get() to
invoke the callback for certain properties.