Make a bunch of API changes.

lib/src/utils.dart

Index: lib/src/utils.dart
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
index 734c58e2687d9706ac1181a40199dc7fee2cb433..af19f90567edd4af1ac411c1f1db0825397ed8ca 100644
--- a/lib/src/utils.dart
+++ b/lib/src/utils.dart
@@ -4,11 +4,20 @@
 
 library oauth2.utils;
 
+import 'dart:convert';
+
+import 'package:crypto/crypto.dart';
+
 /// Adds additional query parameters to [url], overwriting the original
 /// parameters if a name conflict occurs.
 Uri addQueryParameters(Uri url, Map<String, String> parameters) => url.replace(
     queryParameters: new Map.from(url.queryParameters)..addAll(parameters));
 
+String basicAuthHeader(String identifier, String secret) {
+  var userPass = Uri.encodeFull(identifier) + ":" + Uri.encodeFull(secret);
+  return "Basic " + CryptoUtils.bytesToBase64(ASCII.encode(userPass));
+}
+
 /// Like [String.split], but only splits on the first occurrence of the pattern.
 ///
 /// This will always return a list of two elements or fewer.