Simple User management example for Google App Engine?

Question

I am newbie in Google App Engine. While I was going through the tutorial, I found several things that we do in php-mysql is not available in GAE. For example in dataStore auto increment feature is not available. Also I am confused about session management in GAE. Over all I am confused and can not visualize the whole thing.

Please advise me a simple user management system with user registration, user login, user logout, session (create,manage,destroy) with data Store. Also please advise me where I can get simple but effective examples.

Thanks in advance.

Answer 1

I tend to use my own user and session manangement

For my web handlers I will attach a decorator called session and one called authorize. The session decorator will attach a session to every request, and the authorize decorator will make sure that the user is authorised.

(A word of caution, the authorize decorator is specific to how I develop my applications - the username being the first parameter in most requests).

So for example a web handler may look like:

class UserProfile(webapp.RequestHandler):
  @session
  @authorize
  def get(self, user):
     # Do some funky stuff
     # The session is attached to the self object.
     someObjectAttachedToSession = self.SessionObj.SomeStuff
     self.response.out.write("hello %s" % user)

In the above code, the session decorator attaches some session stuff that I need based on the cookies that are present on the request. The authorize header will make sure that the user can only access the page if the session is the correct one.

The decorators code are below:

import functools
from model import Session
import logging

def authorize(redirectTo = "/"):
    def factory(method):
        'Ensures that when an auth cookie is presented to the request that is is valid'
        @functools.wraps(method)
        def wrapper(self, *args, **kwargs):

            #Get the session parameters
            auth_id = self.request.cookies.get('auth_id', '')
            session_id = self.request.cookies.get('session_id', '')

            #Check the db for the session
            session = Session.GetSession(session_id, auth_id)           

            if session is None:
                self.redirect(redirectTo)
                return
            else:
                if session.settings is None:
                    self.redirect(redirectTo)
                    return

                username = session.settings.key().name()

                if len(args) > 0:               
                    if username != args[0]:
                        # The user is allowed to view this page.
                        self.redirect(redirectTo)
                        return

            result = method(self, *args, **kwargs)

            return result
        return wrapper
    return factory

def session(method):
    'Ensures that the sessions object (if it exists) is attached to the request.'
    @functools.wraps(method)
    def wrapper(self, *args, **kwargs):

        #Get the session parameters
        auth_id = self.request.cookies.get('auth_id', '')
        session_id = self.request.cookies.get('session_id', '')

        #Check the db for the session
        session = Session.GetSession(session_id, auth_id)           

        if session is None:
            session = Session()
            session.session_id = Session.MakeId()
            session.auth_token = Session.MakeId()
            session.put()

        # Attach the session to the method
        self.SessionObj = session           

        #Call the handler.          
        result = method(self, *args, **kwargs)

        self.response.headers.add_header('Set-Cookie', 'auth_id=%s; path=/; HttpOnly' % str(session.auth_token))
        self.response.headers.add_header('Set-Cookie', 'session_id=%s; path=/; HttpOnly' % str(session.session_id))

        return result
    return wrapper

def redirect(method, redirect = "/user/"):
    'When a known user is logged in redirect them to their home page'
    @functools.wraps(method)
    def wrapper(self, *args, **kwargs):
        try:    
            if self.SessionObj is not None:
                if self.SessionObj.settings is not None:
                    # Check that the session is correct
                    username = self.SessionObj.settings.key().name()

                    self.redirect(redirect + username)
                    return
        except:
            pass
        return method(self, *args, **kwargs)
    return wrapper