Lift-OpenID should allow extending OpenIdConsumer in a way that only the Attribute-Exchange request and SimpleRegistration request need to be overriden without changing the rest of the code.

I propose that the following methods be extracted (and default to returning None), Option could of course be replaced with Box if that's better.

def reqAttributeExchange(discovered: DiscoveryInformation): Option[FetchRequest] = None
def reqSimpleRegistration(discovered: DiscoveryInformation): Option[SRegRequest] = None

and authRequest be changed like this:

    reqAttributeExchange(discovered) match {
      case Some(fetch) => authReq.addExtension(fetch) 
      case None =>
    }

    reqSimpleRegistration(discovered) match {
      case Some(sreg) => authReq.addExtension(sreg)
      case None =>
    }

The parameter discovered is for the purpose of customizing the requests for certain well-known OpenID providers, whose behaviour and attribute support varies.