This default message is going to be pretty difficult for an end user to understand and cope with.  Would be better to provide a default addressed to the potential end-user who has been directed to log in to CAS via an authentication method that CAS cannot fulfill.  How about something friendlier, like

"Hi. You're trying to log in to <:out value="${service}"/> with a required authentication method of <c:out value="${requiredAuthenticationMethod}"/>.  Unfortunately, CAS doesn't recognize that authentication method and so does not know how to require you to authenticate in that way.  

This is probably a configuration problem either in the application you're trying to log into or in CAS itself. This problem has been logged so that it is available for CAS server administrators to review; you may wish to also engage your local support processes to report this issue and seek resolution.

If you'd like to try to log in *without* requiring a special authentication method, click _here_.  (URL = cas/login?${service} ).  This may not work if the target web application really needs that special authentication method, but it might work and is worth trying once.  Good luck!

If you're a developer or CAS administrator seeing this message: the `authn_method` request parameter had a value not matching any declared in CAS's `argumentExtractorsConfiguration.xml`.  Verify agreement between CAS-using application and CAS server about what custom authentication methods are available and what they are called. :)"