mod_auth_pam is not supported and/or developed any longer. The original author moved on and it mostly works for Apache 1.3 and 2.0. For help with the module, please check the FAQ first (most problems are related to the PAM modules, not to mod_auth_pam itself). If no answer is found, post to the general PAM mailing-list. There are quite a few friendly folks on the list who are able to help.
New maintainers would be very welcome, please apply on the list!
For authentication against /etc/shadow, I recommend mod_authnz_external. For use with LDAP, several LDAP modules are available, choose a recent one.