code: func (idp *IdentityProvider) ServeMetadata(w http.ResponseWriter, r *http.Request) {
  	buf, _ := xml.MarshalIndent(idp.Metadata(), "", "  ")
  	w.Header().Set("Content-Type", "application/samlmetadata+xml")
  	w.Write(buf)
  }
docs: // ServeMetadata is an http.HandlerFunc that serves the IDP metadata