code: public Rcli<CLIENT> clientAs(String apiVersion, ServletRequest req) throws CadiException {
  		Rcli<CLIENT> cl = client(apiVersion);
  		return cl.forUser(transferSS(((HttpServletRequest)req).getUserPrincipal()));
  	}
docs: Use this API when you have permission to have your call act as the end client's ID.
  
  Your calls will get 403 errors if you do not have this permission.  it is a special setup, rarely given.
  
  @param apiVersion
  @param req
  @return
  @throws CadiException