Add a package for authenticating via OAuth2.

pkg/oauth2/lib/src/utils.dart

Index: pkg/oauth2/lib/src/utils.dart
diff --git a/pkg/oauth2/lib/src/utils.dart b/pkg/oauth2/lib/src/utils.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 utils;
+
+import 'dart:uri';
+import 'dart:isolate';
+import 'dart:crypto';
+
+/// Adds additional query parameters to [url], overwriting the original
+/// parameters if a name conflict occurs.
+Uri addQueryParameters(Uri url, Map<String, String> parameters) {
+  var queryMap = queryToMap(url.query);
+  mapAddAll(queryMap, parameters);
+  return url.resolve("?${mapToQuery(queryMap)}");
+}
+
+/// Convert a URL query string (or `application/x-www-form-urlencoded` body)
+/// into a [Map] from parameter names to values.
+Map<String, String> queryToMap(String queryList) {
+  var map = <String>{};
+  for (var pair in queryList.split("&")) {
+    var split = split1(pair, "=");
+    if (split.isEmpty) continue;
+    var key = urlDecode(split[0]);
+    var value = split.length > 1 ? urlDecode(split[1]) : "";
+    map[key] = value;
+  }
+  return map;
+}
+
+/// Convert a [Map] from parameter names to values to a URL query string.
+String mapToQuery(Map<String, String> map) {
+  var pairs = <List<String>>[];
+  map.forEach((key, value) {
+    key = encodeUriComponent(key);
+    value = (value == null || value.isEmpty) ? null : encodeUriComponent(value);
+    pairs.add([key, value]);
+  });
+  return Strings.join(pairs.map((pair) {
+    if (pair[1] == null) return pair[0];
+    return "${pair[0]}=${pair[1]}";
+  }), "&");
+}
+
+/// Add all key/value pairs from [source] to [destination], overwriting any
+/// pre-existing values.
+void mapAddAll(Map destination, Map source) =>
+  source.forEach((key, value) => destination[key] = value);
+
+/// Decode a URL-encoded string. Unlike [decodeUriComponent], this includes
+/// replacing `+` with ` `.
+String urlDecode(String encoded) =>
+  decodeUriComponent(encoded.replaceAll("+", " "));
+
+/// Like [String.split], but only splits on the first occurrence of the pattern.
+/// This will always return a list of two elements or fewer.
+List<String> split1(String toSplit, String pattern) {
+  if (toSplit.isEmpty) return <String>[];
+
+  var index = toSplit.indexOf(pattern);
+  if (index == -1) return [toSplit];
+  return [toSplit.substring(0, index),
+      toSplit.substring(index + pattern.length)];
+}
+
+/// Returns a [Future] that asynchronously completes to `null`.
+Future get async {
+  var completer = new Completer();
+  new Timer(0, (_) => completer.complete(null));
+  return completer.future;
+}