[JDEV] Returning a different response code for non-existent users

[Miguel A.L. Paraz]

Hi,
Sorry for the cross-post between jadmin and jdev - I'm not sure if this is 
an admin thing that can be fixed using configuration, or if it needs coding,
which I'm willing to do.

Right now, a 401/unauthorized error is returned if a user does not exist.
This is the same as if the password is incorrect.
I would like to know how can it be setup that a different 4xx error is 
returned for nonexistent users.

The reason why:
I already have pre-existing dialup users in a RADIUS database.
I already have the contributed mod_auth_radius running.
I want the client to try logging in automatically using the 
dialup username/password.  If the server gives an error that the user is not
yet defined, then the client will register automatically.

With the current setup, the client cannot tell if the 401 is due to
the user not existing, or an incorrect password.

I was trying to trace through the code, and found that it is not the mod_auth_*
module that returns the 401 if the user does not exist.  From the debug
output, I could not easily tell which does the 401.  I'd like to change the
error to the "Not Registered" error or something relevant.

Hints please?  Thanks.