IVOA Recommendation: IVOA Credential Delegation Protocol Version 1.0
  The credential delegation protocol allows a client program to delegate a user's credentials to a service such that that service may make requests of other services in the name of that user. The protocol defines a REST service that works alongside other IVO services to enable such a delegation in a secure manner. In addition to defining the specifics of the service protocol, this document describes how a delegation service is registered in an IVOA registry along with the services it supports. The specification also explains how one can determine from a service registration that it requires the use of a supporting delegation service. 
Matthew Graham, Raymond Plante, Guy Rixon, Giuliano Taffoni
astro-ph.IM