JWT token creation in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the JWT encode function from the correct library.

FastAPI

from jose import [1]

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

Adecode

Bencode

Cjwt

Dtoken

Attempts:

3 left

💡 Hint

Common Mistakes

Importing encode directly instead of jwt module

Using decode instead of jwt

Importing from wrong library

The jwt module from jose provides the encode function to create JWT tokens.

2fill in blank

medium

Complete the code to define the secret key used for signing the JWT token.

FastAPI

SECRET_KEY = '[1]'

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

Ajwtsecret

Bmysecretkey123

C123456

Dtokenkey

Attempts:

3 left

💡 Hint

Common Mistakes

Using an integer instead of a string

Leaving the secret key empty

Using a too simple or insecure key

The secret key is a string used to sign the JWT token securely. Here, 'jwtsecret' is used as an example.

3fill in blank

hard

Fix the error in the code to correctly encode the JWT token with payload and secret key.

FastAPI

token = jwt.[1](payload, SECRET_KEY, algorithm='HS256')

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

Aencode

Bdecode

Csign

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using decode instead of encode

Using a non-existent function like sign or create

Misspelling the function name

The encode function creates a JWT token from the payload and secret key.

4fill in blank

hard

Fill both blanks to create a payload dictionary with username and expiration time.

FastAPI

payload = {'sub': [1], 'exp': [2]

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

A'user123'

Bdatetime.utcnow() + timedelta(minutes=30)

C'admin'

Dtime.time() + 1800

Attempts:

3 left

💡 Hint

Common Mistakes

Using time.time() instead of datetime for expiration

Putting username without quotes

Using wrong keys in the payload

The payload uses 'sub' for the username and exp for expiration time set 30 minutes from now.

5fill in blank

hard

Fill all three blanks to import needed modules and create a JWT token with expiration.

FastAPI

from datetime import [1], [2]

payload = {'sub': 'admin', 'exp': datetime.utcnow() + [3](minutes=15)}
token = jwt.encode(payload, SECRET_KEY, algorithm='HS256')

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

Adatetime

Btimedelta

Dtime

Attempts:

3 left

💡 Hint

Common Mistakes

Importing time instead of timedelta

Using timedelta without import

Confusing datetime and timedelta order

We import datetime and timedelta from datetime module. The expiration uses timedelta(minutes=15).

Practice

1. What is the main purpose of creating a JWT token in FastAPI?

easy

A. To style the user interface

B. To send emails automatically

C. To connect to a database

D. To securely store user information for authentication

Solution

1. Step 1: Understand JWT token purpose

   JWT tokens are used to safely carry user data for authentication.

2. Step 2: Identify correct use in FastAPI

   FastAPI uses JWT tokens to verify user identity securely.

3. Final Answer:

   To securely store user information for authentication -> Option D

4. Quick Check:

   JWT purpose = secure user info [OK]

Hint: JWT tokens are for secure user identity, not UI or DB [OK]

Common Mistakes:

• Confusing JWT with UI styling or database connection
• Thinking JWT sends emails
• Assuming JWT stores passwords directly

2. Which of the following is the correct way to import the function to create JWT tokens in FastAPI using PyJWT?

easy

A. import jwt.encode

B. from fastapi import jwt_encode

C. from jwt import encode

D. from fastapi.security import create_jwt

Solution

1. Step 1: Identify the JWT library used

   PyJWT is commonly used and provides an encode function imported as 'from jwt import encode'.

2. Step 2: Check FastAPI imports

   FastAPI itself does not provide jwt_encode or create_jwt functions directly.

3. Final Answer:

   from jwt import encode -> Option C

4. Quick Check:

   PyJWT encode import = from jwt import encode [OK]

Hint: PyJWT encode is imported from jwt, not fastapi [OK]

Common Mistakes:

• Trying to import JWT functions directly from FastAPI
• Using incorrect import syntax
• Confusing module names

3. Given this code snippet, what will be the output of the print(token) statement?

from jwt import encode

payload = {"user_id": 123}
secret = "mysecret"
algorithm = "HS256"
token = encode(payload, secret, algorithm=algorithm)
print(token)

medium

A. A JWT token string encoded with user_id 123

B. An error because algorithm parameter is missing

C. The original payload dictionary printed

D. None, because encode returns nothing

Solution

1. Step 1: Understand encode function behavior

   The encode function creates a JWT token string from the payload using the secret and algorithm.

2. Step 2: Analyze the code snippet

   Payload and secret are provided correctly, algorithm is set to HS256, so encode returns a JWT token string.

3. Final Answer:

   A JWT token string encoded with user_id 123 -> Option A

4. Quick Check:

   encode returns JWT string [OK]

Hint: encode returns a token string, not the original data [OK]

Common Mistakes:

• Expecting encode to print the payload
• Missing algorithm causes error (not true here)
• Thinking encode returns None

4. Identify the error in this JWT token creation code snippet:

from jwt import encode

payload = {"user_id": 42}
secret = "secretkey"
token = encode(payload, secret)
print(token)

medium

A. Missing algorithm parameter causes an error

B. No error; code runs correctly

C. Secret key should be bytes, not string

D. Payload must be a string, not a dictionary

Solution

1. Step 1: Check encode function requirements

   PyJWT's encode has a default algorithm='HS256', so it is not strictly required.

2. Step 2: Analyze the code snippet

   The code calls encode with payload and secret; algorithm defaults to HS256, so it runs correctly and produces a token.

3. Final Answer:

   No error; code runs correctly -> Option B

4. Quick Check:

   Algorithm defaults to HS256 = no error [OK]

Hint: PyJWT encode defaults to HS256 algorithm [OK]

Common Mistakes:

• Assuming algorithm defaults to HS256
• Thinking payload must be string
• Believing secret must be bytes

5. You want to create a JWT token in FastAPI that expires in 30 minutes. Which code snippet correctly adds the expiration time to the payload before encoding?

hard

A. payload = {"user_id": 1, "exp": datetime.utcnow() + timedelta(minutes=30)}

B. payload = {"user_id": 1, "exp": str(datetime.utcnow() + timedelta(minutes=30))}

C. payload = {"user_id": 1, "exp": time.time() + 1800}

D. payload = {"user_id": 1, "exp": datetime.now() + timedelta(minutes=30)}

Solution

1. Step 1: Understand JWT expiration format

   The 'exp' claim must be a UTC datetime or a timestamp representing expiration time.

2. Step 2: Evaluate each option

   payload = {"user_id": 1, "exp": datetime.utcnow() + timedelta(minutes=30)} uses datetime.utcnow() + timedelta for 30 minutes, which is correct. payload = {"user_id": 1, "exp": str(datetime.utcnow() + timedelta(minutes=30))} converts datetime to string, which is invalid. payload = {"user_id": 1, "exp": time.time() + 1800} uses time.time() but JWT expects datetime or timestamp as int, so this may cause issues. payload = {"user_id": 1, "exp": datetime.now() + timedelta(minutes=30)} uses datetime.now() which is local time, not UTC, causing potential errors.

3. Final Answer:

   payload = {"user_id": 1, "exp": datetime.utcnow() + timedelta(minutes=30)} -> Option A

4. Quick Check:

   Use UTC datetime for 'exp' claim [OK]

Hint: Use datetime.utcnow() + timedelta for expiration [OK]

Common Mistakes:

• Using local time instead of UTC
• Converting datetime to string for 'exp'
• Using wrong time functions like time.time() without conversion