MOD_BUT requires other components, before you can test it by yourself. The login application is important, because it will send MOD_BUT LOGON=OK after successful authentication and afterwards, the client can reach the backend application.
I have created a demo application, so you can see and test MOD_BUT without actually downloading, compiling, installing and integrating everything. Seems to me much more easy to fully understand MOD_BUT.
You can test via HTTP (SSL is currently disabled)
by using the following user credentials:
Username mod_but
Password demo