Exercising Challenge/Response code path in pam client?

[Richard Perrin]

Hi,

I'm seeking a simple as possible config for freeradius server (version
2.1.12+dfsg-1.2ubuntu8.1 in Ubuntu 14.04) that would allow me to
exercise the Challenge/Response path in the pam client (packaged as
libpam-radius-auth-1.3.17).

I see PW_ACCESS_CHALLENGE in several modules, but I haven't made the
leap on how to configure the server to have pam-radius-auth (currently
successfully authenticating against the server) receive an
Access-Challenge instead of Accept/Reject. My end goal is verification
of the client side code, rather than a production server deployment.
Could you please provide me with guidance?

Thanks Alan, and others, for both these pieces of software.

- Richard Perrin