Specify the callback function to use in the server to inform the
client of the cipher suites supported. The DES and 3DES ciphers
must be supported for interoperability. It is currently used by
the DIGEST-MD5 mechanism. The function can be later retrieved
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.