A WebID is an HTTP URI that denotes ("refers to" or names) an agent on HTTP based networks e.g., the Web or an enterprise Intranet. In line with Linked Data principles, when you de-reference (lookup) a WebID it resolves to profile document that describes its referent (what it denotes). The aforementioned profile document consists of RDF model based structured data, constructed using terms from the FOAF vocabulary.
Profile documents can be stored on your own Web server, with access constained to specific agent identities via the use of access controls, if need be. In effect, preserving the privacy of the profile document's subject.
The WebID+TLS protocol (formerly known as FOAF+SSL) is a decentralized secure authentication protocol that uses the profile information as well as the Transport Layer Security client certificates available in virtually all modern web browsers. It was first presented  for the W3C Workshop on the Future of Social Networking in 2009.
Contrary to the usual SSL usage patterns, it does not require a dedicated Certificate authority to perform the user authorization. Useful identities can be minted for users easily by themselves using any TLS certificate (even self-signed ones). The authentication to Web sites using TLS client certificates doesn't usually require that the user inputs a password, which makes WebID+TLS quite convenient, as an alternative to other single sign-on mechanisms. However, there are issues of user friendliness in the client certificates selection dialogues in popular Web browsers, which tend to render their use difficult at times.
A WebID+TLS-based web of trust connecting all the user's activity on the World Wide Web could be established gradually, without formal key signing parties, to make the identity more trustworthy and hard for anyone (even the original issuing authority) to forge.
- W3C WebID Incubator Group
- FOAF+SSL decentralized authentication protocol.
- "foaf+ssl: adding security to open distributed social networks". Sun Microsystems.
- "Workshop on the Future of Social Networking". Barcelona, ES: W3C. January 2009.
- "foaf+ssl: creating a web of trust without key signing parties". Sun Microsystems.
- Gamble, Matthew; Goble, Carole (April 2010), "Standing on the Shoulders of the Trusted Web: Trust, Scholarship and Linked Data", Proceedings of the WebSci10: Extending the Frontiers of Society On-Line