def login_url(service_url=request.url)
      url = URI(Rails.application.cas_server_url)
      url.path = "/login"
      url.query = "service=#{service_url || request.url}"
      url.to_s
    end
def login_url(service_url=request.url)
      url = URI(Rails.application.cas_server_url)
      url.path = "/login"
      url.query = "service=#{service_url || request.url}"
      url.to_s
    end
Renders the CAS login URL with re-direct back to some URL.
 @param service_url [String] Optional url to redirect to after authentication.
 @return [String] The CAS login URL.