Upgrade to shelf 0.6.0.

lib/src/oauth2.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library pub.oauth2;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:oauth2/oauth2.dart';
@@ skipping 165 matching lines @@
       authorizationEndpoint,
       tokenEndpoint,
       httpClient: httpClient);
 
   // Spin up a one-shot HTTP server to receive the authorization code from the
   // Google OAuth2 server via redirect. This server will close itself as soon as
   // the code is received.
   var completer = new Completer();
   bindServer('localhost', 0).then((server) {
     shelf_io.serveRequests(server, (request) {
-      if (request.url.path != "/") {
+      if (request.url.path.isNotEmpty) {
         return new shelf.Response.notFound('Invalid URI.');
       }
 
       log.message('Authorization received, processing...');
       var queryString = request.url.query;
       if (queryString == null) queryString = '';
 
       // Closing the server here is safe, since it will wait until the response
       // is sent to actually shut down.
       server.close();
@@ skipping 11 matching lines @@
         'In a web browser, go to $authUrl\n'
         'Then click "Allow access".\n\n'
         'Waiting for your authorization...');
   });
 
   return completer.future.then((client) {
     log.message('Successfully authorized.\n');
     return client;
   });
 }