WebFinger
WebFinger is a protocol specified by the Internet Engineering Task Force IETF in RFC 7033 that allows for discovery of information about people and things identified by a URI. Information about a person might be discovered via an acct: URI, for example, which is a URI that looks like an email address. WebFinger is specified as the discovery protocol for OpenID Connect, which is a protocol that allows one to more easily log in to various sites on the Internet.