[horde] authentication active directory with fallback

[Ken Weaverling]

Quoting Guido Leisker <lists.gl at guido-leisker.de>:

> 2. Would it be possible to make a fallback to textlogin
> (ldap/mysql/unix) if the 1st doesnt work, maybe because the active
> directory is down, or he/she still has no account there?

If horde is authenticating against your imap server and that imap 
server is using PAM to authenticate, then it's possible to set up 
multiple authentication sources in PAM with fallback.

For example, if using latest Redhat release of linux, run the 
"system-config-authentication" tool and just check off all the services 
that you'd like authentication to work with.

Be aware that that will modify the system-auth pam file and hence 
effect all of your services on that server though. What we did was just 
use that to build the correct pam file on a test box, then just named 
that imap and copied that over the imap file in the /etc/pam.d dir.