added hint about oidc refresh-token

auth/oidc.go

@@ -82,6 +82,9 @@ func NewOIDCBackend(cfg *OIDCConfig) (b *OIDCBackend, err error) {
 	return
 }
 
+// TODO: implement session refresh go-routine
+//       see: https://github.com/golang/oauth2/issues/84
+
 func (b *OIDCBackend) CallbackHandler() http.Handler {
 	return &oidcCallbackHandler{backend: b}
 }