Authenticating Users

This part of the Python Guestbook code walkthrough shows how to authenticate users and display a customized greeting for the signed-in user.

This page is part of a multi-page tutorial. To start from the beginning and see instructions for setting up, go to Creating a Guestbook.

Signing in users

The MainPage class defines a handler for HTTP GET requests to the root path '/'. The handler checks to see whether a user is signed in:

guestbook.py 
class MainPage(webapp2.RequestHandler):

    def get(self):
        guestbook_name = self.request.get('guestbook_name',
                                          DEFAULT_GUESTBOOK_NAME)
        greetings_query = Greeting.query(
            ancestor=guestbook_key(guestbook_name)).order(-Greeting.date)
        greetings = greetings_query.fetch(10)

        user = users.get_current_user()
        if user:
            url = users.create_logout_url(self.request.uri)
            url_linktext = 'Logout'
        else:
            url = users.create_login_url(self.request.uri)
            url_linktext = 'Login'

        template_values = {
            'user': user,
            'greetings': greetings,
            'guestbook_name': urllib.quote_plus(guestbook_name),
            'url': url,
            'url_linktext': url_linktext,
        }

        template = JINJA_ENVIRONMENT.get_template('index.html')
        self.response.write(template.render(template_values))

If the user is already signed in to your application, the get_current_user() method returns a User object, and the app displays the users's nickname. If the user has not signed in, the code redirects the user's browser to the Google account sign-in screen. The Google account sign-in mechanism sends the user back to the app after the user has signed in.

For more information, see the Users API.

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