code: func (s *Server) SAMLLogin(w http.ResponseWriter, r *http.Request) {
  	if s.ServiceProvider == nil {
  		http.NotFound(w, r)
  		return
  	}
  
  	// TODO(ejholmes): Handle error
  	_ = s.ServiceProvider.InitiateLogin(w)
  }
docs: // SAMLLogin starts a Service Provider initiated login. It generates an
  // AuthnRequest, signs the generated id and stores it in a cookie, then starts
  // the login with the IdP.