Transform the string typed into the login form into a tentative Principal Name to be
validated by a specific type of Authentication Handler.
The Principal Name eventually assigned by the CredentialsToPrincipalResolver may
be unqualified ("AENewman"). However, validation of the Principal name against a
particular backend source represented by a particular Authentication Handler may
require transformation to a temporary fully qualified format such as
AENewman@MAD.DCCOMICS.COM or MAD\AENewman. After validation, this form of the
Principal name is discarded in favor of the choice made by the Resolver.
- Parameters:
formUserId - The raw userid typed into the login form
- Returns:
- the string that the Authentication Handler should lookup in the backend system