Add OAuth2 support for end users (i.e. 3-legged flow with the browser).

git_cl.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 from distutils.version import LooseVersion
@@ skipping 2044 matching lines @@
     # TODO(ukai): is it ok for gerrit case?
     base_branch = args[0]
   else:
     if cl.GetBranch() is None:
       DieWithError('Can\'t upload from detached HEAD state. Get on a branch!')
 
     # Default to diffing against common ancestor of upstream branch
     base_branch = cl.GetCommonAncestorWithUpstream()
     args = [base_branch, 'HEAD']
 
+  # Make sure authenticated to Rietveld before running expensive hooks. It is
+  # a fast, best efforts check. Rietveld still can reject the authentication
+  # during the actual upload.
+  if not settings.GetIsGerrit() and auth_config.use_oauth2:
+    authenticator = auth.get_authenticator_for_host(
+        cl.GetRietveldServer(), auth_config)
+    if not authenticator.has_cached_credentials():
+      raise auth.LoginRequiredError(cl.GetRietveldServer())
+
   # Apply watchlists on upload.
   change = cl.GetChange(base_branch, None)
   watchlist = watchlists.Watchlists(change.RepositoryRoot())
   files = [f.LocalPath() for f in change.AffectedFiles()]
   if not options.bypass_watchlists:
     cl.SetWatchers(watchlist.GetWatchersForPaths(files))
 
   if not options.bypass_hooks:
     if options.reviewers or options.tbr_owners:
       # Set the reviewer list now so that presubmit checks can access it.
@@ skipping 1097 matching lines @@
     return 2
 
   # Reload settings.
   global settings
   settings = Settings()
 
   colorize_CMDstatus_doc()
   dispatcher = subcommand.CommandDispatcher(__name__)
   try:
     return dispatcher.execute(OptionParser(), argv)
+  except auth.AuthenticationError as e:
+    DieWithError(str(e))
   except urllib2.HTTPError, e:
     if e.code != 500:
       raise
     DieWithError(
         ('AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
           'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
   return 0
 
 
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   colorama.init()
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)