As Jamie said it would require custom development. You might be able to find some useful code examples on codeplex if you search for active directory, however typically it requires a more privileged user to query AD. I'm not sure it is advisable to integrate such code into a web app for security reasons, it may introduce new attack vectors for gaining access to secure info in AD that would otherwise be more protected, as with many things just because its possible doesn't mean its a good idea so use your own judgment about whether you really want to do that kind of thing. 

Internally mojoPortal uses its own roles so you would have to have corresponding role names in mojoPortal and then assign those corresponding roles to the mojoPortal user. There is no way without forking the code (which is not recommended) to use AD roles directly.