Try to authenticate a user given the login information passed to
the factory in the
AuthenticationContext
. There are three
outcomes from this method:
- The login request was valid: An
AuthenticationInformation
object should
be returned with at least the external id of the user.
- The login request was invalid: An
AuthenticationException
(or a
subclass) should be thrown
- It was not possible to know if the request was invalid or not: null should
be returned to let the authentication continue with another action or internal
authentication.