Add a package for authenticating via OAuth2.

pkg/oauth2/lib/src/handle_access_token_response.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 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.
+final int _EXPIRATION_GRACE = 10;

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

"final int" -> "const".

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

Done.

+
+/// 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);
+
+  var contentType = response.headers['content-type'];
+  if (contentType != null) {
+    contentType = new ContentType.fromString(contentType);
+  }
+  if (contentType == null || contentType.value != "application/json") {
+    throw new FormatException('Invalid OAuth response for '
+        '"$tokenEndpoint": content-type was "$contentType", expected '
+        '"application/json".');
+  }
+
+  var parameters;
+  try {
+    parameters = JSON.parse(response.body);
+  } catch (e) {

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

Restrict this:

} on FormatException catch (e) {

You really don't want to catch NoSuchMethod or OutOfMemory here. :)

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

JSON.parse doesn't throw a FormatException :-/.

[Bob Nystrom, 2012/11/19 21:37:10]

Restrict it to a JSONParseException? We definitely don't want a catch-all here.

[nweiz, 2012/11/19 22:20:11]

It doesn't throw a JSONParseException either :-/. It just throws a generic
string error.

+    throw new FormatException('Invalid OAuth response for '
+        '"$tokenEndpoint": invalid JSON.\n\n${response.body}');

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

How about a helper function for all of these throws:

validate(bool condition, String message) {
  if (!condition) throw new FormatException('Invalid OAuth response for '
       '"$tokenEndpoint": $message.\n\n${response.body}');
}

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

Done.

+  }
+
+  for (var requiredParameter in ['access_token', 'token_type']) {
+    if (!parameters.containsKey(requiredParameter)) {
+      throw new FormatException('Invalid OAuth response for '
+          '"$tokenEndpoint": did not contain required parameter '
+          '"$requiredParameter".\n\n${response.body}');
+    } else if (parameters[requiredParameter] is! String) {
+      throw new FormatException('Invalid OAuth response for '
+          '"$tokenEndpoint": required parameter "$requiredParameter" was '
+          'not a string, was "${parameters[requiredParameter]}".\n\n'
+          '${response.body}');
+    }
+  }
+
+  // TODO(nweiz): support the "mac" token type
+  // (http://tools.ietf.org/html/draft-ietf-oauth-v2-http-mac-01)
+  if (parameters['token_type'].toLowerCase() != 'bearer') {
+    throw new FormatException('Invalid OAuth response for '
+        '"$tokenEndpoint": unknown token type '
+        '"${parameters['token_type']}".\n\n${response.body}');
+  }
+
+  var expiresIn = parameters['expires_in'];
+  if (expiresIn != null && expiresIn is! int) {
+      throw new FormatException('Invalid OAuth response for '
+          '"$tokenEndpoint": parameter "expires_in" was not an int, was '
+          '"$expiresIn".\n\n${response.body}');
+  }
+
+  for (var name in ['refresh_token', 'scope']) {
+    var value = parameters[name];
+    if (value == null || value is String) continue;
+    throw new FormatException('Invalid OAuth response for "$tokenEndpoint": '
+        'parameter "$name" was not a string, was "$value".\n\n'
+        '${response.body}');
+  }
+
+  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) {
+  // 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${response.body}');
+  }
+
+  var contentType = response.headers['content-type'];
+  if (contentType != null) {
+    contentType = new ContentType.fromString(contentType);
+  }
+  if (contentType == null || contentType.value != "application/json") {
+    throw new FormatException('Invalid OAuth response for "$tokenEndpoint": '
+        'content-type was "$contentType", expected "application/json".');
+  }
+
+  var parameters;
+  try {
+    parameters = JSON.parse(response.body);
+  } catch (e) {
+    throw new FormatException('Invalid OAuth response for '
+        '"$tokenEndpoint": invalid JSON.\n\n${response.body}');
+  }
+
+  if (!parameters.containsKey('error')) {
+    throw new FormatException('Invalid OAuth response for "$tokenEndpoint": '
+        'did not contain required parameter "error".\n\n${response.body}');
+  } else if (parameters["error"] is! String) {
+    throw new FormatException('Invalid OAuth response for "$tokenEndpoint": '
+        'required parameter "error" was not a string, was '
+        '"${parameters["error"]}"\n\n${response.body}.');
+  }
+
+  for (var name in ['error_description', 'error_uri']) {
+    var value = parameters[name];
+    if (value == null || value is String) continue;
+    throw new FormatException('Invalid OAuth response for "$tokenEndpoint": '
+        'parameter "$name" was not a string, was "$value".\n\n'
+        '${response.body}');
+  }
+
+  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);
+}