cas: Make it easier to override finalStep() in subclasses.
cas: Make it easier to override finalStep() in subclasses.

This patch makes it easier to override the finalStep()-function in
subclasses by making sure that the casValidation()-function can be used
from subclasses.

Patch by Josselin Jacquard.

Rud5G/simplesamlphp,Rud5G/simplesamlphp,Rud5G/simplesamlphp,Rud5G/simplesamlphp