Flask how to redirect to previous page after successful login

Question

I have a webapp where I don't use Flask-login. If user visit a link and is not logged in, I redirect the user to login page. I achieve this my setting 'username' in session and checking that when user tries to access some link directly without logging in i.e in that case username will be null.

I have tried to follow this SO solution, but the next parameter is always None. I have tried both solution but can't get either one to work.

username = session.get('username')
if username:
    # go to home 
else:
    next_url = request.url
    login_url = '%s?next=%s' % (url_for('login'), next_url)
    return redirect(login_url)

Second solution

username = session.get('username')
if username:
    # go to home 
else:
    return redirect(url_for('login', next= request.url))

print (request.url) = localhost:5000/visitPage

Login Function

   if 'next' in request.args:
     return redirect(next)
   else:
     return redirect(url_for("user.index"))

Here when I print (next), it is None
But login url has next argument

http://localhost:5000/login?next=http%3A%2F%2Flocalhost%3A5000%2FvisitPage

Solution 1

There may be several problems:

• url_for skips query param if it has None value
• your login endpoint takes POST requests. In such case you have to get the next param such way request.form.get('next')

If these tips do not help you, you can put import ipdb;ipdb.set_trace() (may be you have to install ipdb first) in your code and try to debug it for better understanding what is going on here or put more context for understanding your problem.

Solution 2

Use session to keep track of the previous url, for example:

@app.route('/profile')
def profile():
    if user_not_logged_in:
        session['url'] = url_for('profile')
        return redirect(url_for('login'))
    return rendertemplate('profile.html')

@app.route('/login')
def login():
    if login == True: #assuming login was successful
         if 'url' in session:
            return redirect(session['url'])
         return redirect(url_for('anyother_url'))

Comments

[jas]

Issue was in Login function. Login func does form validation and redirected the user if form data is invalid. So, in this case first call to login function resulted in re-direct and the next data was gone on second request. Had to save the next data between the two request and everything worked fine.