Credential Validation Modules

 CVM is a framework for validating a set of credentials against a database
 using a filter program. The modules act as a filter, taking a set of
 credentials as input and writing a set of facts as output if those
 credentials are valid. Optional input is given to the module through
 environment variables.
 .
 Some of the ideas for CVM came from experience with PAM (pluggable
 authentication modules), the checkpassword interface used by qmail-pop3d,
 and the "authmod" interface used by Courier IMAP and POP3. This framework
 places fewer restrictions on the invoking client than checkpassword does,
 and is much simpler to implement on both sides than PAM and the authmod
 framework.
 .
 See http://untroubled.org/cvm/cvm.html for more information.