One of the most common areas of functionality in any web application is the use of authentication. Basically it's away of allowing your users & visitors to register, and then have permission-based access to certain tools and data. There are many ways to implement this, but why re-invent the wheel?
If your company is using LDAP to store employee information and authentication data, you can interface with that as your access control mechanism. And rather that building it from scratch, you can use this open source LDAP class to start with!