1. A method performed by an authentication server for authenticating a subscriber, the method comprising: receiving a request message including a plurality of attributes having respective attribute names and respective attribute values; retrieving an authentication profile object; identifying a plurality of authentication attributes to use for authentication from said authentication profile object; extracting said plurality of authentication attribute values from said message; pre-processing one or more of said extracted attribute values; and authenticating said request message based on said pre-processed extracted attribute values.