Readjust the MFA branching logic to clearly reflect that authentication ...

...method requested is tied to the webflow.

This pull is strongly related to issue https://github.com/Unicon/cas-mfa/issues/11. It demonstrates that authentication methods are and should be tied to webflow events concretely. Subsequently pulls on https://github.com/Unicon/cas-mfa/issues/11 will also demonstrate adding a second authentication method tied to different set of events and handlers to fully prove this functionality.