Add a package for authenticating via OAuth2.

pkg/oauth2/lib/src/handle_access_token_response.dart

Index: pkg/oauth2/lib/src/handle_access_token_response.dart
diff --git a/pkg/oauth2/lib/src/handle_access_token_response.dart b/pkg/oauth2/lib/src/handle_access_token_response.dart
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+++ b/pkg/oauth2/lib/src/handle_access_token_response.dart
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+// 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 handle_access_token_response;
+
+import 'dart:io';
+import 'dart:json';
+import 'dart:uri';
+
+import '../../../http/lib/http.dart' as http;
+
+import 'credentials.dart';
+import 'authorization_exception.dart';
+
+/// The amount of time, in seconds, to add as a "grace period" for credential
+/// expiration. This allows credential expiration checks to remain valid for a
+/// reasonable amount of time.
+const _EXPIRATION_GRACE = 10;
+
+/// Handles a response from the authorization server that contains an access
+/// token. This response format is common across several different components of
+/// the OAuth2 flow.
+Credentials handleAccessTokenResponse(
+    http.Response response,
+    Uri tokenEndpoint,
+    Date startTime,
+    List<String> scopes) {
+  if (response.statusCode != 200) _handleErrorResponse(response, tokenEndpoint);
+
+  void validate(bool condition, String message) =>
+    _validate(response, tokenEndpoint, condition, message);
+
+  var contentType = response.headers['content-type'];
+  if (contentType != null) {
+    contentType = new ContentType.fromString(contentType);
+  }
+  validate(contentType != null && contentType.value == "application/json",
+      'content-type was "$contentType", expected "application/json"');
+
+  var parameters;
+  try {
+    parameters = JSON.parse(response.body);
+  } catch (e) {
+    validate(false, 'invalid JSON');
+  }
+
+  for (var requiredParameter in ['access_token', 'token_type']) {
+    validate(parameters.containsKey(requiredParameter),
+        'did not contain required parameter "$requiredParameter"');
+    validate(parameters[requiredParameter] is String,
+        'required parameter "$requiredParameter" was not a string, was '
+        '"${parameters[requiredParameter]}"');
+  }
+
+  // TODO(nweiz): support the "mac" token type
+  // (http://tools.ietf.org/html/draft-ietf-oauth-v2-http-mac-01)
+  validate(parameters['token_type'].toLowerCase() == 'bearer',
+      '"$tokenEndpoint": unknown token type "${parameters['token_type']}"');
+
+  var expiresIn = parameters['expires_in'];
+  validate(expiresIn == null || expiresIn is int,
+      'parameter "expires_in" was not an int, was "$expiresIn"');
+
+  for (var name in ['refresh_token', 'scope']) {
+    var value = parameters[name];
+    validate(value == null || value is String,
+        'parameter "$name" was not a string, was "$value"');
+  }
+
+  var scope = parameters['scope'];
+  if (scope != null) scopes = scope.split(" ");
+
+  var expiration = expiresIn == null ? null :
+      startTime.add(new Duration(seconds: expiresIn - _EXPIRATION_GRACE));
+
+  return new Credentials(
+      parameters['access_token'],
+      parameters['refresh_token'],
+      tokenEndpoint,
+      scopes,
+      expiration);
+}
+
+/// Throws the appropriate exception for an error response from the
+/// authorization server.
+void _handleErrorResponse(http.Response response, Uri tokenEndpoint) {
+  void validate(bool condition, String message) =>
+    _validate(response, tokenEndpoint, condition, message);
+
+  // OAuth2 mandates a 400 or 401 response code for access token error
+  // responses. If it's not a 400 reponse, the server is either broken or
+  // off-spec.
+  if (response.statusCode != 400 && response.statusCode != 401) {
+    var reason = '';
+    if (response.reasonPhrase != null && !response.reasonPhrase.isEmpty) {
+      ' ${response.reasonPhrase}';
+    }
+    throw new FormatException('OAuth request for "$tokenEndpoint" failed '
+        'with status ${response.statusCode}$reason.\n\n${response.body}');
+  }
+
+  var contentType = response.headers['content-type'];
+  if (contentType != null) {
+    contentType = new ContentType.fromString(contentType);
+  }
+  validate(contentType != null && contentType.value == "application/json",
+      'content-type was "$contentType", expected "application/json"');
+
+  var parameters;
+  try {
+    parameters = JSON.parse(response.body);
+  } catch (e) {
+    validate(false, 'invalid JSON');
+  }
+
+  validate(parameters.containsKey('error'),
+      'did not contain required parameter "error"');
+  validate(parameters["error"] is String,
+      'required parameter "error" was not a string, was '
+      '"${parameters["error"]}"');
+
+  for (var name in ['error_description', 'error_uri']) {
+    var value = parameters[name];
+    validate(value == null || value is String,
+        'parameter "$name" was not a string, was "$value"');
+  }
+
+  var description = parameters['error_description'];
+  var uriString = parameters['error_uri'];
+  var uri = uriString == null ? null : new Uri.fromString(uriString);
+  throw new AuthorizationException(parameters['error'], description, uri);
+}
+
+void _validate(
+    http.Response response,
+    Uri tokenEndpoint,
+    bool condition,
+    String message) {
+  if (condition) return;
+  throw new FormatException('Invalid OAuth response for "$tokenEndpoint": '
+      '$message.\n\n${response.body}');
+}