You probably want to look into Net::LDAP.

After you validate the user, you'll want to look into something like How can I maintain a session cookie?

Well, one way to handle the authentication requirements of a web-site, in an LDAP-based intranet environment, is to simply let the web server protect the entire site.   Both Apache and (especially...) IIS can do this.   The web server has the magical means to determine who the requesting internal user is, and of course to distinguish internal users from outsiders.   Unauthorized users simply can’t reach the site at all.   Furthermore, those that do, have available credentials that the CGI program can query if further authentication logic within the site needs to use it.   (Internet users are automatically excluded.)

This is one key way in which “intra-net” web sites are able to play by very different and much-simplified rules, versus those of the “wild and wooly” Internet-at-large.   If you simply want to restrict the entire site, you don’t have to write protective logic into the site at all.   The site is inside the fortress, and they’re checking badges at the door, and there’s no other way to get inside, and ... and that’s it.   (“Schweet!”)