Hi Alex
You certainly can using phpbb - there is the authphpbb3 plug in available. It has some issues but I have it successfully running with a version 3.0 phpbb forum. I have yet to try it with the new version 3.1 of phpbb which is structurally different, but looking at the plugin code, I think it should work okay. Here are details on the plugin
authphpbb3.
Martin