App Engine remote_api with OpenID

Question

I\'ve recently tried to switch my app engine app to using openID, but I\'m having an issue authenticating with remote_api. The old authentication mechanism for remote_api doesn\

Answer 1

This is definitely an issue... mark your interest in getting Google to fix this by starring the ticket at http://code.google.com/p/googleappengine/issues/detail?id=3258 and feel free to add any of your workarounds there.

On a related note, we also recognize that the docs are somewhat sparse, so I'm working on an article which hopefully fills-in some of those holes... stay tuned and keep your eyes open at http://code.google.com/appengine/articles

Answer 2

This was a fun one.

Looking at remote_api, the flow for authentication seems to be something like this:

• Prompt the user for Google credentials
• Post the credentials to https://www.google.com/accounts/ClientLogin
• Parse the auth token out of the response body
• Pass the token to https://myapp.appspot.com/_ah/login
• Grab ACSID cookie set in the response
• Pass the ACSID cookie in subsequent requests that require authorization

I couldn't find a lot of documentation on the new OpenID support, though Nick's blog entry was informative.

Here's the test app I wrote to see how things work:

app.yaml:

handlers:
- url: /remote_api
  script: $PYTHON_LIB/google/appengine/ext/remote_api/handler.py
  login: admin
- url: /.*
  script: test.py

test.py:

class MainPage(webapp.RequestHandler):
  def get(self):
    user = users.get_current_user()
    if user:
      self.response.out.write("Hi, %s!<hr>admin is %s" % (user.user_id(),
        users.is_current_user_admin()))
    else:
      self.redirect(users.create_login_url('/', None,
        'https://www.google.com/accounts/o8/id'))

Flipping my auth mode between Google Accounts and Federated Login, I noticed a few things:

• Admin users are correctly recognized by is_current_user_admin() with OpenID
• Mixing modes doesn't work. With authentication set to Google Accounts, calling create_login_url with a federated_identity throws a NotAllowedError
• An ACSID cookie is still produced at the end of the login process, only it comes from /_ah/openid_verify instead of /_ah/login

So what's happening with remote_api when using Federated Login? If we're using the default appengine_rpc.HttpRpcServer, it's dutifully following the same Google Account authentication process described at the top, only the app no longer considers the ACSID cookie returned by /_ah/login to be valid, so since you're still unauthenticated, you get a 302 redirect to the OpenID login page, /_ah/login_required.

I dunno what the right solution is here. Seems like it would require an API update. Maybe Nick or one of the other Googlers can weigh in.

For now, here's a hacky workaround:

• Turn on Federated Login for your app
• Make sure you're passing save_cookies=True when calling remote_api_stub.ConfigureRemoteDatastore for your console script
• Attempt console authentication and get the 302 error
• Login as an admin via your app's web interface
• In your browser cookies, find the ACSID cookie for myapp.appspot.com
• Find and edit your local ~/.appcfg_cookies file
• Replace the ACSID cookie for myapp.appspot.com with the one from your browser

The next time you try to use remote_api, it should work without prompting for credentials. You'll have to repeat the last 4 steps every time the cookie expires, though. You can bump the expiration from 1 day to as high as 2 weeks in the admin console to minimize the annoyance. Have fun!

Answer 3

Here's a workaround you can use until there's a more permanent solution in place.