Email verification pattern in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask class.

Flask

from flask import [1]

Drag options to blanks, or click blank then click option'

AFlask

BRequest

Crender_template

Dredirect

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request instead of Flask

Using lowercase flask instead of Flask

The Flask class is imported from the flask module to create the app.

2fill in blank

medium

Complete the code to define a route for email verification.

Flask

@app.route('/verify_email/[1]')
def verify_email(token):
    pass

Drag options to blanks, or click blank then click option'

Atoken

Bemail

Cuser

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name in the route and function

Not including a variable in the route

The route uses a variable part named 'token' to capture the verification token from the URL.

3fill in blank

hard

Fix the error in the code to generate a timed token for email verification.

Flask

from itsdangerous import URLSafeTimedSerializer

def generate_token(email):
    serializer = URLSafeTimedSerializer(app.config['SECRET_KEY'])
    return serializer.[1](email, salt=app.config['SECURITY_PASSWORD_SALT'])

Drag options to blanks, or click blank then click option'

Asign

Bloads

Cdumps

Dunsign

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'loads' instead of 'dumps' to create a token

Using 'sign' or 'unsign' which are not methods of URLSafeTimedSerializer

The 'dumps' method creates a signed token from the email string.

4fill in blank

hard

Fill both blanks to decode the token and handle expiration.

Flask

def confirm_token(token, expiration=3600):
    serializer = URLSafeTimedSerializer(app.config['SECRET_KEY'])
    try:
        email = serializer.[1](token, salt=app.config['SECURITY_PASSWORD_SALT'], max_age=[2])
    except Exception:
        return False
    return email

Drag options to blanks, or click blank then click option'

Aloads

Bexpiration

Csign

Dunsign

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dumps' to decode the token

Not passing the expiration time correctly

'loads' decodes the token and 'max_age' sets the expiration time in seconds.

5fill in blank

hard

Fill all three blanks to send a verification email with a token link.

Flask

from flask_mail import Message

def send_verification_email(user_email):
    token = generate_token(user_email)
    verify_url = url_for('verify_email', token=[1], _external=True)
    msg = Message('Please verify your email', sender=app.config['MAIL_DEFAULT_SENDER'], recipients=[user_email])
    msg.body = f'Click the link to verify your email: [2]'
    mail.[3](msg)

Drag options to blanks, or click blank then click option'

Atoken

Bverify_url

Csend

Dsend_message

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'send_message' instead of 'send'

Passing the wrong variable to url_for

Not using the verification URL in the email body

The token variable is passed to the URL, the URL is used in the email body, and 'send' sends the email message.

Practice

1. What is the main purpose of email verification in a Flask application?

easy

A. To store user data securely in the database

B. To confirm that the user owns the provided email address

C. To speed up the login process

D. To encrypt the user's password

Solution

1. Step 1: Understand email verification purpose

   Email verification is used to confirm that the user actually owns the email they provided during signup.

2. Step 2: Differentiate from other security tasks

   Encrypting passwords and speeding login are different tasks unrelated to email verification.

3. Final Answer:

   To confirm that the user owns the provided email address -> Option B

4. Quick Check:

   Email verification = Confirm ownership [OK]

Hint: Email verification confirms user email ownership [OK]

Common Mistakes:

• Confusing email verification with password encryption
• Thinking it speeds up login
• Assuming it stores data securely

2. Which Flask library is commonly used to create timed tokens for email verification?

easy

A. flask_sqlalchemy

B. flask_login

C. itsdangerous

D. flask_mail

Solution

1. Step 1: Identify token generation library

   The itsdangerous library provides URLSafeTimedSerializer to create timed tokens.

2. Step 2: Differentiate from other Flask extensions

   flask_sqlalchemy manages databases, flask_login handles user sessions, and flask_mail sends emails but does not create tokens.

3. Final Answer:

   itsdangerous -> Option C

4. Quick Check:

   Token creation = itsdangerous [OK]

Hint: Use itsdangerous for timed token creation [OK]

Common Mistakes:

• Choosing flask_mail for token creation
• Confusing flask_login with token generation
• Selecting flask_sqlalchemy incorrectly

3. Given this Flask code snippet, what will verify_token(token) return if the token is expired?

from itsdangerous import URLSafeTimedSerializer, SignatureExpired

serializer = URLSafeTimedSerializer('secret-key')

def verify_token(token):
    try:
        email = serializer.loads(token, max_age=3600)
        return email
    except SignatureExpired:
        return None

medium

A. Returns None

B. Raises a SignatureExpired exception

C. The email string inside the token

D. Returns an empty string

Solution

1. Step 1: Understand token verification logic

   The function tries to load the token with a max age of 3600 seconds (1 hour).

2. Step 2: Handle expired token exception

   If the token is expired, it raises SignatureExpired, which is caught and returns None.

3. Final Answer:

   Returns None -> Option A

4. Quick Check:

   Expired token returns None [OK]

Hint: Expired tokens return None in try-except block [OK]

Common Mistakes:

• Expecting exception to propagate
• Assuming it returns empty string
• Thinking it returns the email anyway

4. Identify the error in this Flask email verification token generation code:

from itsdangerous import URLSafeTimedSerializer

serializer = URLSafeTimedSerializer('secret-key')

def generate_token(email):
    token = serializer.dumps(email)
    return token

# Later verification
email = serializer.loads(token, max_age=3600)

medium

A. Token variable is undefined at verification

B. Missing secret key in serializer initialization

C. max_age parameter is invalid in loads()

D. Using dumps() instead of loads() to verify

Solution

1. Step 1: Check token generation and usage

   The token is generated inside generate_token but not stored or passed outside.

2. Step 2: Verify token usage scope

   At verification, token is used but not defined in that scope, causing a NameError.

3. Final Answer:

   Token variable is undefined at verification -> Option A

4. Quick Check:

   Undefined token variable causes error [OK]

Hint: Ensure token variable is defined before verification [OK]

Common Mistakes:

• Ignoring variable scope for token
• Thinking secret key is missing
• Misusing max_age parameter

5. You want to implement email verification in Flask so that users receive a link with a token that expires after 24 hours. Which approach correctly combines token creation, sending email, and verification?

hard

A. Generate token without secret key, send email, verify token ignoring expiration

B. Store plain email in database, send email without token, verify by matching email only

C. Send token as plain text in email body, verify token with max_age=3600

D. Generate token with URLSafeTimedSerializer, send email with token link, verify token with max_age=86400

Solution

1. Step 1: Create token with expiration

   Use URLSafeTimedSerializer with a secret key to generate a token that expires after 86400 seconds (24 hours).

2. Step 2: Send email with token link and verify properly

   Send the token inside a URL link in the email. Verify the token using loads() with max_age=86400 to enforce expiration.

3. Final Answer:

   Generate token with URLSafeTimedSerializer, send email with token link, verify token with max_age=86400 -> Option D

4. Quick Check:

   Token creation + email + 24h expiry = Generate token with URLSafeTimedSerializer, send email with token link, verify token with max_age=86400 [OK]

Hint: Use max_age=86400 for 24h token expiry [OK]

Common Mistakes:

• Not using tokens in email links
• Ignoring token expiration
• Sending tokens without secret key