The created SecurityToken shoud respect the validity passed from the IdP

A SecurityToken has a lifetime. AuthServices should compute the lifetime based on the validity of the assertion(s) from the IdP.
There should also be a good fallback if no condition is present in the assertion.
And last but not least AuthServices should provide the default override mechanism of WIF. That way it is even possible to implement sliding sessions in an RP.

The changes I made will respect the validity of the assertion and implements the same fallback and override mechanism as WIF together with MS WsFederationModule.