From FusionForge Wiki

See : https://fusionforge.org/tracker/index.php?func=detail&aid=311&group_id=6&atid=114

WebID is a proposed standard to integrate the use of SSL client certs and FOAF (to describe a person's profile) in order to provide an authentication "token" for Web services.

A possible implementation of the "consumer" of WebID profiles (aka Service Provider / SP) part in FusionForge could be made using libAuthentication