The Courier authentication library provides authentication services for
other Courier applications.  In this context, the term "authentication"
refers to the following functions:

    1. Take a userid or a loginid, and a password. Determine whether the
       loginid and the password are valid.
    2. Given a userid, obtain the following information about the userid:

         A. The account's home directory.
         B. The numeric system userid and groupid that owns all files
            associated with this account.
         C. The location of the account's maildir.
         D. Any maildir quota defined for this account. See the Courier
            documentation for more information on maildir quotas.
         E. Other miscellaneous account-specific options.

    3. Change the password associated with a loginid.
    4. Obtain a complete list of all loginids.

Homepage:
https://www.courier-mta.org/authlib/
