monline

Basically you'll need the mod_auth_pam module (the libapache2-mod-auth-pam package in Debian) and the mod_auth_sys_group module (the libapache2-mod-auth-sys-group package in Debian). The latter is only needed in case you want to authenticate against groups and not just users.

The configuration is pretty well described on the mod_auth_pam website. Here's a sample config entry:

The AuthBasicAuthoritative Off directive is required to make mod_auth_pam work with recent Apache versions too. The AuthUserFile /dev/null directive prevents some error messages from appearing in the Apache error log.