I use and Active Directory web service for identifying the user and also being able to access their informaiton in AD such as manager, email, location, dept, etc., this works great with a UDC in a browser form.
Here are the details
http://www.qdabra.com/en/products/ADWebService.aspx
Otherwise their are some ways to get some identitiy information out of SharePoint but this is more challenging with browser forms.