Introduce authentication service.

services/authentication/authentication.mojom

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+[JavaPackage="org.chromium.mojo.authentication"]
+module authentication;
+
+interface AuthenticationService {
+  // Request an account to use.

[ppi, 2015/04/29 13:32:23]

s/Request/Requests/

[tonyg, 2015/04/29 13:47:43]

This interface could probably use a little more robust documentation. For
instance, I assume that a null username means it failed or the user cancelled,
but the comment should clarify how to treat null.

[qsr, 2015/04/29 14:22:19]

Done.

[qsr, 2015/04/29 14:22:20]

 Added documentation, and human readable error messages.

 We will probably want some error code some day, but this is not something I
feel we are ready for yet.

+  SelectAccount() => (string? username);
+  // Request an oauth2 token for the given account with the given scopes.

[ppi, 2015/04/29 13:32:23]

s/Request/Requests/

[qsr, 2015/04/29 14:22:20]

Done.

+  GetOAuth2Token(string username, array<string> scopes) => (string? token);
+  // Request to clear a previously acquired token. This should be called when a

[ppi, 2015/04/29 13:32:23]

s/Request/Requests/

[qsr, 2015/04/29 14:22:19]

Done.

+  // token is refused by a server component before requesting a new token to
+  // clear the token from any cache.
+  ClearOAuth2Token(string token);
+};