Server Authentication Context Lifecycle

The authentication context is used with a sequence of calls during the authentication process, this task is to look into how we can apply a lifecycle to that so that appropriate clean up can be performed.

This could be closely related to ELY-35 which specifically looks at outcome notification.

When considering a lifecycle I think we have two key events to think about, the most natural one being once the authentication process is complete regardless of outcome - however should also consider intermediate responses going back to the client - we do not want to be holding onto expensive resources once we pass control back to the client as that risks a Dos based attack.