Access Apache LDAP authentication details in PHP
Today I was working on a small web application that will run on a corporate intranet. There was an existing LDAP server and many existing web apps use the authentication details cached in the browser (Basic Authentication) to identify a user and determine access levels.
My application is written in PHP and I wanted to leverage this same mechanism to determine the current user and customize my application. Since my searches on Google didn’t pull up anything similar, I want to document what I did.
I did explore the possibility of using PHP’s LDAP library to perform the authentication but decided instead to use the basic authentication provided by Apache. I have two reasons for this. First is that most users are accustomed to this already and developers of other internal applications are familiar with this approach. Second is that authentication details are more easily cached for a long duration, which cuts down on reauthentication. In a trusted intranet environment this is very desirable.
To begin with, I installed and configured Apache on Ubuntu Linux. One of the modules that wasn’t enabled by default is authnz_ldap. I did notice that it was available so I ran this command to enable the module:
$ sudo a2enmod authnz_ldap
$ sudo /etc/init.d/apache2 restart
With this module installed I then needed to give it some details about my LDAP server and what paths I wanted protected by LDAP authentication. I accomplished this by adding a <Location> directive to the httpd.conf file. This is what my Location directive looked like:
AuthName "My Application"
After making this change another restart was necessary. At this point I reloaded a page that was protected and was able to authenticate as expected.
PHP Access to authentication
This is surprisingly easy (and surprisingly undocumented anywhere that I could find). PHP will automatically populate several $_SERVER superglobal keys with the authentication values cached in Apache. The key values are:
Later I found that you can also add additional values to AuthLDAPURL that will populate additional keys in your $_SERVER superglobal.
At this point you might choose to perform additional operations against the LDAP server using PHP’s library or simply use the available values to customize your intranet web application.