Is it possible for Flask to redirect with parameters?

February 19, 2024

I have two apps which are both launched by Flask, app1 and app2. In app2, I need to redirect to a url defined in app1 and pass a parameter(I need logged_in in the template).

If it was in the same app, I can do this by

from flask import Flask, render_template, redirect, url_for

app1 = Flask(__name__)


@app1.route('/')
def index():
   return render_template('index.html', logged_in=False)

@app1.get('/login')
def login():
   return redirect(url_for('index', logged_in=True))

However, I cannot do this in app2, let’s say.

from flask import Flask, redirect

app2 = Flask(__name__)

@app2.get('/login')
def login():
   return redirect('http://localhost:5000', logged_in=True) # this is not allowed.

Anyone has an idea? Thanks in advance.

>Solution :

You can use a query parameter when redirecting:

@app2.get('/login')
def login():
   return redirect('http://localhost:5000?logged_in=1')

And on the localhost server you can use Javascript to change the page based on the query param:

const urlParams = new URLSearchParams(window.location.search);
const loggedIn = urlParams.get('logged_in') == '1';
alert(loggedIn);

Or, if the localhost server is also running Flask, you can get the query params like so:

from flask import request

@app.route('/')
def root():
    logged_in = request.args.get('logged_in') == '1'
    return render_template('index.html', logged_in=logged_in)