I'm using session expiration in Flask. Ideally I would like to flash appropriate message after session expires and redirect to login page. It seems like there is no way to get expiry information from the cookie to test for that or am I missing something?
If the session has expired, the session cookie is no longer present in the browser.
From the docs, session is a python dictionary.
The session object works pretty much like an ordinary dict...
For, example, You set the session by: session['username'] = 'xxxxxx'.
To check if that cookie is still available, use session.get('username'). If it returns None, the cookie is absent, else, the cookie is present.
The check becomes:
if not session.get('user'):
flash('Not so fast! Kindly login to view that page')
return redirect(url_for('login'))
else:
#...Do something with logged-in user
Flask-Login and Flask-Session are two extensions that handle user login and sessions very well for you.
Related
I have been given a task to authenticate admin login programmatically and logout as well.
I am able to to do login but on logged out when I check which user I am logging out it says AnonymousUser. How can I make sure I log out current user which is logged it.
I am using Django REST framework and testing it on Postman.
#api_view(["POST"])
def adminLogin(request):
if(request.method=="POST"):
username = request.data["username"]
password = request.data["password"]
authenticated_user = authenticate(request,username=username, password=password)
if authenticated_user != None:
if(authenticated_user.is_authenticated and authenticated_user.is_superuser):
login(request,authenticated_user)
return JsonResponse({"Message":"User is Authenticated. "})
else:
return JsonResponse({"message":"User is not authenticated. "})
else:
return JsonResponse({"Message":"Either User is not registered or password does not match"})
#api_view(["POST"])
def adminLogout(request):
print(request.user)
logout(request)
return JsonResponse({"message":"LoggedOut"})
Logging in/logging out with a REST API makes not much sense. The idea of logging in/logging out, at least how Django implements it, is by means of the session, so with a cookie that has the session id.
API clients like Postman usually do not work with cookies: each request is made more or less independent of the previous one. If you thus make the next request without a reference to the session, then the view will not link a user to that request. Clients like AJAX that runs on the browser of course can work with cookies, since these are embedded in the browser that manages cookies. You can work with cookies in postman as specified in this tutorial [learning postman], but this is usually not how an API is supposed to work.
This is why APIs usually work with a token, for example a JWT token. When authenticating, these are given a token that might be valid for a short amount of time, and subsequently it uses that token to make any other request that should be authorized.
As the Django REST framework documentation on TokenAuthentication [drf-doc] says, you can define views that create, and revoke tokens. The page also discusses session authentication that thus can be used for AJAX requests.
But likely you are thus using the wrong means to do proper authentication for your REST API, and you thus might want to work with a token like a JWT token instead.
I am using Flask-login with remember=False (the only cookie is the session cookie). When copy-pasting the session cookie after logging out, for some reason the session is still valid and the user is logged in. Even though the logged out session was deleted properly in the flask logout_user() function - meaning that the ["user_id"] was deleted from the session dictionary. It seems like the session is restored from the old cookie. can someone explain?
I do not really have a right answer for this yet, as I am investigating it myself, but there are a couple of points I would like to make here:
the logout_user() from Flask-login does not really seem to be invalidating the session. It just changes the 'session' cookie's value in the client (the browser). While in the backend this session is still alive.
An experiment to prove this would be: (a simple browser plugin like CookieManager can be used to perform this exercise)
login to the app
take a note of the 'session' cookie's value post successful login
now logout
now observer the 'session' cookie's value again. And you would
notice that it has now changed.
Replace this value with the 'session'cookie's value previously noted
in step 1 above.
Try visiting an internal authenticated page again.
Result : You would successfully be able to view an internal page without re-logging in, proving that the logout_user() never really invalidated the session but just changed the 'session' cookie in the client.
Howeverm, I am myself still taking a look into flask-login logout_user() definition and trying to make sense of it.
I had This issue too. After diagnosing what i found is the decorator #login_required *does not invalidate the User in server side after logout*, which is a security threat. This will be a cake walk for a Hacker to hack your application since they can easily extract all the request and header data from developer tool of your browser and can again send request to you server from outside of the application.For ex: If you have used any API in your application the it will be very easy for Hacker to get all the request data and resend a request using POSTMAN.
I solved this issue by creating a separate decorator "#authentication_required" and used in place of "#login_required". then it worked for me,though #login_required is supposed to do the same.
So basically while logging in i generated a random string(token) and sent to database and same string(token) is added to session of flask i.e session["token"]="akhfkjdbfnd334fndf" use any random string generator function.(session object is globally available if u r using flask . u can very well add any field to session). and while logout i again generate a string(token) and update the old token with newly generated token in database. So what #authentication_required will do is it will get the token from session object and the token which is present in database and try to compare the value. if both are same then only #authentication_required will let the client access api.and dont forget to do session.clear() after logout_user().
#---------------------------------------------------------------#
##authentication_required definition
def authentication_required(f):
#wraps(f)
def wrap(*args, **kwargs):
try:
user_id=session['user_id'] #assigning "user_id" from flask session object to a variable "user_id"
user=User_table.find_first(_id=user_id)#couhdb query syntax
#comparing api_token sent to session object at the login time with api_token in sent to database at login time. If both doesn't matches then user is redirected to login page.
if not session["token"]==user.token:
return redirect(url_for('login'))
else:
return f(*args, **kwargs)
except:
app.logger.info(Response('Request Did not came through header !', 401, {'WWW-Authenticate': 'Login failed'}))
return redirect(url_for('login_to system'))
return wrap
#---------------------------------------------------------------#
-------------------------------------------------------
login api code
#app.route('/login_to_system', methods=['GET', 'POST'])
def login_to_system():
form = LoginForm()
user = User_table.find_first(username=form.username.data)
login_user(user, remember=False)
try:
#Generating an random api_token at login time and will send to db
token_string=''.join(random.choices(string.ascii_uppercase + string.digits, k=14))
user.token=token_string #assigning token_string value to field api_token in database.
user.save() #saving the value in user table(using couch Db You can follow syntax as per you DB)
except Exception as error:
app.logger.error(str(error))
app.logger.info("before setting api_token in session")
session["token"]= token_string #adding a "token" to session object
#app.logger.info("Rendering login form")
return render_template('login.html', title='Sign In', form=form)
#-------------------------------------------------------#
#-----------------------------------#
#logout api code
#app.route('/logout')
def logout():
try:
user=User_table.find_first(_id=user_id)
#Generating a random token while logging out and will overwrite eariler token sent at login time send to database.
user.token=token_string=''.join(random.choices(string.ascii_uppercase + string.digits, k=17))
user.save()
except Exception as error:
app.logger.error(str(error))
logout_user()
session.clear()#clearing session
return redirect(url_for('Home page'))
#-----------------------------------#
Note: Seems like login_required is not working fine for me thats why i had to create another decorator but login_required also does the same thing but its strange that it not working for me.
I have a form with csrf token that works.
There is also a button to upload a picture via ajax and put the url into a textarea of the first form on the same page. I have some js inplace to set the csrf value and the button also works fine.
If the user is logged in there is absolutely no problem when using first the button to insert the image url and then saving the form.
But when I have a visitor who is not logged in there is a problem: When he uploads a picture a new account is automatically created and the visitor is logged in without him doing anything.
while True:
try:
random_password = User.objects.make_random_password()
random_username = str(uuid.uuid1().hex)[:5]
new_temp_user = User.objects.create_user(random_username, password=random_password)
except IntegrityError:
pass
else:
new_user = authenticate(username=random_username,password=random_password)
login(request,new_user)
break
Since this is done via Ajax he doesn't notice any change to the website he is seeing. Only the url of the uploaded picture gets added to the first form. On the server side he is now a registered user, but he doesn't see it yet. Now when he submits the form the csrf validation fails. The form still has the csrf token in place, but somehow it became invalid.
I suspect that the login process has some influence over the csrf token. Any ideas what I may do about it?
EDIT: I checked some more and it seems that the problem is due to the login. Every login seems to change the csrf value. Now when the user gets a login over ajax the token in the form doesn't update. What may be the best way to update it?
The csrf token is rotated when the user logs in. This was added as a security measure in Django 1.5.2 (release notes).
After the ajax request, you might be able to fetch the new csrf token from the cookie, and update the form in the DOM. Alternatively, you could refresh the page after the user is logged in.
def myview(request):
item = Item.objects.all().count()
if not request.COOKIES.get('mycookie', None):
response.set_cookie('mycookie', item)
n = request.COOKIES.get('mycookie')
return render_to_response('index.html', {'n': n}, context_instance=RequestContext(request))
It seems that my cookies are not saved. What am I doing wrong?
When you set a cookie, this is a request for the client (the browser) to store this information in its cookie storage.
Highly simplified, it works like this:
You tell your code, set a cookie.
Your code tells the browser, hey set this cookie.
Browser says, okay its set.
On the next request, browser will send the cookie back to you.
It will be available for reading on any requests after the request where you set it. So when you refresh the page, the cookie will be "readable" by your code.
For my website pretty much every page has a header bar displaying "Welcome, ABC" where "ABC" is the username. That means request.user will be called for every single request resulting in database hits over and over again.
But once a user is logged in, I should be able to store his user instance in his cookie and encrypt it. That way I can avoid hitting the database repeatedly and just retrieve request.user from the cookie instead.
How would you modify Django to do this? Is there any Django plugins that does what I need?
Thanks
You want to use the session middleware, and you'll want to read the documentation. The session middleware supports multiple session engines. Ideally you'd use memcached or redis, but you could write your own session engine to store all the data in the user's cookie. Once you enable the middleware, it's available as part of the request object. You interact with request.session, which acts like a dict, making it easy to use. Here are a couple of examples from the docs:
This simplistic view sets a has_commented variable to True after a user posts a comment. It doesn’t let a user post a comment more than once:
def post_comment(request, new_comment):
if request.session.get('has_commented', False):
return HttpResponse("You've already commented.")
c = comments.Comment(comment=new_comment)
c.save()
request.session['has_commented'] = True
return HttpResponse('Thanks for your comment!')
This simplistic view logs in a "member" of the site:
def login(request):
m = Member.objects.get(username=request.POST['username'])
if m.password == request.POST['password']:
request.session['member_id'] = m.id
return HttpResponse("You're logged in.")
else:
return HttpResponse("Your username and password didn't match.")
This smells of over-optimisation. Getting a user from the db is a single hit per request, or possibly two if you use a Profile model as well. If your site is such that an extra two queries makes a big difference to performance, you may have bigger problems.
The user is attached to the request object using the Authentication Middleware provided by django (django.contrib.auth.middleware). It users a function the get_user function in django.contrib.auth.init to get the user from the backend you are using. You can easily change this function to look for the user in another location (e.g. cookie).
When a user is logged in, django puts the userid in the session (request.session[SESSION_KEY]=user.id). When a user logs off, it erases the user's id from the session. You can override these login and logoff functions to also store a user object in the browsers cookie / erase user object from cookie in the browser. Both of these functions are also in django.contrib.auth.init
See here for settting cookies: Django Cookies, how can I set them?
Once you have proper caching the number of database hits should be reduced significantly - then again I'm not really and expert on caching. I think it would be a bad idea to modify request.user to solve your problem. I think a better solution would be to create some utility, method or custom template tag that attempts to load your require user data from the cookie, and return the result. If the user data is not found in the cookie, then a call to request.user should be made, save the data to the cookie, and then return the result. You could possibly use a post_save signal to check for changes to the user data, so that you can make update to the cookie as required.