Write an OAuth2Callback for my AppEngine application

Question

I want to make this scenario happen in an AppEngine application:

When the user requests MyPageHandler, he'll be automatically redirected to a login page (if he's not logged in). Then if the user doesn't not exist in our records, we'll ask him for giving us some credentials (more precisely those specified by https://www.googleapis.com/auth/plus.login ).We store the authorized token for future use. The next time the user connects, he logs in directly.

For this I wrote this code:

decorator = appengine.OAuth2DecoratorFromClientSecrets(
    'my_client_secret.json',
    scope = 'https://www.googleapis.com/auth/plus.login')

@decorator.oauth_aware
def custom_login_required(handler_method):

    def check_login(self, *args, **kwargs):
        user = users.get_current_user()

        if not user:
            return self.redirect(users.create_login_url(self.request.url))
        else:
            usrs = UsersModel.query(UsersModel.email == users.get_current_user().email()).fetch()

            if len(usrs) == 0:
                user = UsersModel(email =  users.get_current_user().email())
                http = decorator.Http()
                myService = build('plus', 'v1', developerKey=api_key, http = http)
                people_resource = service.people()
                people_document = people_resource.get(userId='me').execute()
                user.gplus_profile = people_document['url']
                user.put()
                handler_method(self, *args, **kwargs)
            else:
                #get the link and avatar
                handler_method(self, *args, **kwargs)

    return check_login

class MyPage(webapp2.RequestHandler):
    @custom_login_required
    def get(self):
         .
         .
         #Some Work
         .
         .

class OAuth2CallbackRequestHandler(decorator.callback_handler()):
    def get(self):
         #I do not know how to make use of this
         pass

Thank you.

Answer 1

I finally managed to create the OAuth2CallbackHandler to fit the scenario I already specified in my post. Here is the solution for people having the same issue.

class OAuth2CallbackRequestHandler(webapp2.RequestHandler):

@decorator.oauth_aware
def get(self):

    user = users.get_current_user()
    if not user:  #user not signed in
        return self.redirect(users.create_login_url(self.request.url))
    else:         #user signed-in
        usrs = UsersModel.query(UsersModel.email == users.get_current_user().email()).fetch()

        if len(usrs) == 0: #NEW USER
            if len(self.request.get('code')) != 0:  #user gave us permission
                credentials = decorator.flow.step2_exchange(self.request.get('code'))  #exchange user-permissions for credentials
                decorator.set_credentials(credentials)
                if decorator.has_credentials():  #ensuring credentials are setup
                    http = decorator.http()
                    myService = build('plus', 'v1', developerKey = api_key, http = http)

                    user = UsersModel(email =  users.get_current_user().email())
                    people_resource = myService.people()
                    people_document = people_resource.get(userId='me').execute()
                    user.gplus_profile_url = people_document['url']
                    user.gplus_avatar_url = people_document['image']['url']
                    user.display_name = people_document['displayName']
                    user.access_token = credentials.access_token
                    user.refresh_token = credentials.refresh_token #You may need them if you want to update the current information

                    user.put()

                    return self.redirect('/MyPage')
                else:
                    return self.redirect('/oauth2callback')
            else:  #we ask user for permission
                link = decorator.authorize_url()
                return self.redirect(link)

        else:   #USER ALREADY EXISTS
            return self.redirect('/MyPage')


class MyPage(webapp2.RequestHandler):

def get(self):

    if not users.get_current_user():
        self.redirect('/oauth2callback')
        return

    # Continue your work here

Answer 2

Look at

https://developers.google.com/accounts/docs/OAuth2WebServer

You first do the stuff in the part Forming the URL, then you make the call out to google, then your callback (specified in the redirect_uri parameter) does the stuff in Handling the Response section.

Or, perhaps better, check and see if there is a library that does the dirty work for you.