WebFinger
https://webfinger.net/
WebFinger is used to discover information about people or other entities on the Internet that are identified by a URI using standard Hypertext Transfer Protocol (HTTP) methods over a secure transport. A WebFinger resource returns a JavaScript Object Notation (JSON) object describing the entity that is queried. The JSON object is referred to as the JSON Resource Descriptor (JRD).
Setting Up a WebFinger Server
http://www.packetizer.com/webfinger/server.html
WebFinger is designed to be a very simple protocol that allows for automated service discovery. Further, it was designed so that any domain owner could run his or her own WebFinger server.