There currently seems to be no (easy) way of checking credentials without actually logging in a user.

There is a $login parameter in the Horde_Core_Auth_Application::authenticate method which is then passed to the authenticate method of the base/parent auth class, but it is not used anywhere in the Horde_Auth_Base::authenticate method.

If there is already a way to just check credentials, please let me know.

Maybe this issue would be better in the horde/auth repo, but issues are not enabled there.