Remember me functionality in Flask - Step-by-Step Execution

Concept Flow - Remember me functionality

User submits login form

↓

Check credentials

↓

Is 'Remember me' checked?

No→Create session cookie

|Yes↓

Create persistent cookie with token

↓

Send cookie to browser

↓

User closes browser

↓

User returns

↓

Check persistent cookie

↓

Auto-login user

↓

Grant access

↓

END

This flow shows how the app checks login, sets session or persistent cookies, and auto-logs in returning users with 'Remember me'.

Execution Sample

Flask

from flask import Flask, request, make_response
app = Flask(__name__)

@app.route('/login', methods=['POST'])
def login():
    username = request.form['username']
    remember = 'remember' in request.form
    resp = make_response('Logged in')
    if remember:
        resp.set_cookie('remember_token', 'abc123', max_age=30*24*60*60)
    else:
        resp.set_cookie('session', 'xyz789')
    return resp

This code logs in a user and sets a persistent cookie if 'Remember me' is checked, else a session cookie.

Execution Table

Step	Action	Input	Condition	Cookie Set	Output
1	User submits login form	username='user1', remember checked	N/A	N/A	Proceed to check credentials
2	Check credentials	username='user1'	Valid user?	N/A	Credentials valid
3	Check 'Remember me'	remember=True	Is remember checked?	N/A	Yes branch
4	Set cookie	remember=True	Set persistent cookie?	remember_token=abc123 (30 days)	Cookie set with token
5	Send response	N/A	N/A	remember_token cookie sent	Response sent to browser
6	User closes browser	N/A	N/A	Cookie remains (persistent)	Browser closed
7	User returns	Cookie remember_token=abc123	Cookie valid?	N/A	Auto-login user
8	Grant access	N/A	N/A	N/A	User logged in automatically
9	End	N/A	N/A	N/A	Process complete

💡 Process ends after user is auto-logged in or session cookie expires.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 7	Final
username	None	'user1'	'user1'	'user1'	'user1'	'user1'	'user1'
remember	False	False	True	True	True	True	True
cookie_set	None	None	None	'remember_token=abc123'	'remember_token=abc123'	'remember_token=abc123'	'remember_token=abc123'
user_logged_in	False	False	False	False	False	True	True

Key Moments - 3 Insights

Why does the cookie persist after closing the browser when 'Remember me' is checked?

Because the cookie is set with a max_age (30 days), making it persistent. See execution_table step 4 where 'remember_token=abc123' is set with max_age.

What happens if 'Remember me' is not checked?

A session cookie is set without max_age, so it expires when the browser closes. This is shown in the else branch in the code and implied in execution_table step 3 'No' branch.

How does the app auto-login the user on return?

The app reads the persistent cookie 'remember_token' and validates it. If valid, it logs in the user automatically as shown in execution_table step 7.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what cookie is set when 'Remember me' is checked?

A No cookie is set

B 'session=xyz789' session cookie

C 'remember_token=abc123' with 30 days expiry

D 'remember_token=xyz789' session cookie

💡 Hint

Check the 'Cookie Set' column at step 4 in execution_table.

At which step does the user get auto-logged in on return?

A Step 5

B Step 7

C Step 3

D Step 2

💡 Hint

Look for 'Auto-login user' in the 'Output' column of execution_table.

If the 'Remember me' box is not checked, what changes in the cookie behavior?

A A session cookie is set that expires on browser close

B A persistent cookie is still set

C No cookie is set at all

D The cookie expires immediately

💡 Hint

Refer to key_moments about what happens if 'Remember me' is not checked and execution_table step 3.

Concept Snapshot

Remember me functionality in Flask:
- On login, check if 'Remember me' is checked.
- If yes, set a persistent cookie with max_age (e.g., 30 days).
- If no, set a session cookie that expires on browser close.
- On user return, check persistent cookie to auto-login.
- Use cookies to keep user logged in beyond session.

Full Transcript

This visual execution trace shows how a Flask app handles 'Remember me' functionality. When a user logs in, the app checks credentials and whether the 'Remember me' checkbox is selected. If selected, it sets a persistent cookie with a token and a long expiry time. If not, it sets a session cookie that expires when the browser closes. When the user returns, the app checks for the persistent cookie and auto-logs in the user if the token is valid. The execution table details each step, showing actions, conditions, and cookies set. The variable tracker follows key variables like username, remember flag, cookie set, and login status. Key moments clarify common confusions about cookie persistence and auto-login. The quiz tests understanding of cookie setting and login flow. This helps beginners see how 'Remember me' works step-by-step in Flask.