'Return the User-Id corresponding to a CURVE client\'s public key
Default implementation uses the z85-encoding of the public key.
Override to define a custom mapping of public key : user-id
This is only called on successful authentication.
Parameters
client_public_key: bytes
The client public key used for the given message
Returns
user_id: unicode
The user ID as text'

def curve_user_id(self, client_public_key):

    return z85.encode(client_public_key).decode('ascii')
