Update handlers.go

Compare secrets just on not public clients

Signed-off-by: Miguel Martinez <martinezcanteromiguel@gmail.com>

server/handlers.go

@@ -813,7 +813,7 @@ func (s *Server) withClientFromStorage(w http.ResponseWriter, r *http.Request, h
 		return
 	}
 
-	if subtle.ConstantTimeCompare([]byte(client.Secret), []byte(clientSecret)) != 1 {
+	if !client.Public && subtle.ConstantTimeCompare([]byte(client.Secret), []byte(clientSecret)) != 1 {
 		if clientSecret == "" {
 			s.logger.Infof("missing client_secret on token request for client: %s", client.ID)
 		} else {