Add a package for authenticating via OAuth2.

pkg/oauth2/lib/src/authorization_exception.dart

Index: pkg/oauth2/lib/src/authorization_exception.dart
diff --git a/pkg/oauth2/lib/src/authorization_exception.dart b/pkg/oauth2/lib/src/authorization_exception.dart
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@@ -0,0 +1,36 @@
+// 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 authorization_exception;
+
+import 'dart:io';
+
+/// An exception raised when OAuth2 authorization fails.
+class AuthorizationException {

[Bob Nystrom, 2012/11/16 19:53:30]

extends Exception

Or implements?

[nweiz, 2012/11/17 01:06:27]

Done.

+  /// The name of the error. Possible names are enumerated in [the spec][].
+  ///
+  /// [the spec]: http://tools.ietf.org/html/draft-ietf-oauth-v2-31#section-5.2
+  final String error;
+
+  /// The description of the error, provided by the server. This is optional.

[Bob Nystrom, 2012/11/16 19:53:30]

Will it be `null` or `""` if not provided?

[nweiz, 2012/11/17 01:06:27]

null. Made this clear in the docs.

+  final String description;
+
+  /// A URI for a page that describes the error in more detail, provided by the
+  /// server. This is optional.
+  final Uri uri;
+
+  /// Creates an AuthorizationException.
+  AuthorizationException(this.error, this.description, this.uri);
+
+  /// Provides a string description of the AuthorizationException.
+  String toString() {
+    var header = 'OAuth authorization error ($error)';
+    if (description != null) {
+      header = '$header: $description';
+    } else if (uri != null) {
+      header = '$header: $uri';
+    }
+    return '$header.';

[Bob Nystrom, 2012/11/16 19:53:30]

I think I'd prefer to rely on the description having it's own period. Leave this
off?

[nweiz, 2012/11/17 01:06:27]

I haven't actually seen any OAuth2 providers that actually give descriptions
with their errors, but I suspect they're just short strings rather than full
punctuated sentences.

+  }
+}