Protected routes in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the FastAPI class.

FastAPI

from fastapi import [1]
app = [1]()

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

AFastAPI

BRequest

CDepends

DHTTPException

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request instead of FastAPI

Using Depends in place of FastAPI

The FastAPI class is imported to create the app instance.

2fill in blank

medium

Complete the code to create a dependency that checks for a token.

FastAPI

from fastapi import Depends, HTTPException, Header

def get_token(token: str = [1]):
    if token != "secret":
        raise HTTPException(status_code=401, detail="Unauthorized")
    return token

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AHeader(None)

BQuery(None)

CCookie(None)

DBody(None)

Attempts:

3 left

💡 Hint

Common Mistakes

Using Query instead of Header for token

Using Body which expects JSON payload

Header(None) extracts the token from HTTP headers for authentication.

3fill in blank

hard

Fix the error in the route to use the dependency correctly.

FastAPI

@app.get("/protected")
async def protected_route(token: str = [1]):
    return {"token": token}

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ADepends(get_token())

Bget_token()

CDepends(get_token)

Dget_token

Attempts:

3 left

💡 Hint

Common Mistakes

Calling get_token inside Depends with parentheses

Passing get_token without Depends

Depends expects the function itself, not a call, so use Depends(get_token).

4fill in blank

hard

Fill both blanks to create a protected POST route that requires a token.

FastAPI

@app.post("/submit")
async def submit_data(data: dict, token: str = [1]):
    return {"data": data, "token": [2]

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

ADepends(get_token)

Btoken

CDepends(get_token())

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using Depends(get_token()) with parentheses

Referencing data instead of token in the return

The token parameter uses Depends(get_token) and the returned token is referenced by its name.

5fill in blank

hard

Fill all three blanks to create a protected route that raises an error if token is missing or invalid.

FastAPI

from fastapi import Header, HTTPException

async def get_token(token: str = [1]):
    if not token:
        raise HTTPException(status_code=401, detail=[2])
    if token != "secret":
        raise HTTPException(status_code=403, detail=[3])
    return token

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

AHeader(None)

B"Token missing"

C"Invalid token"

DQuery(None)

Attempts:

3 left

💡 Hint

Common Mistakes

Using Query instead of Header

Raising wrong status codes or messages

Use Header(None) to get the token, and raise HTTPException with appropriate messages for missing or invalid tokens.

Practice

1. What is the main purpose of protected routes in FastAPI?

easy

A. To automatically generate API documentation

B. To speed up the API response time

C. To allow anyone to access all endpoints without restrictions

D. To restrict access to certain endpoints by verifying user credentials

Solution

1. Step 1: Understand what protected routes do

   Protected routes limit access to certain parts of an app by checking if the user is allowed.

2. Step 2: Identify the correct purpose

   Only To restrict access to certain endpoints by verifying user credentials describes restricting access by verifying user credentials, which matches protected routes.

3. Final Answer:

   To restrict access to certain endpoints by verifying user credentials -> Option D

4. Quick Check:

   Protected routes = restrict access [OK]

Hint: Protected routes check user access before allowing endpoint use [OK]

Common Mistakes:

• Thinking protected routes improve speed
• Confusing protected routes with documentation features
• Assuming protected routes allow open access

2. Which FastAPI feature is commonly used to enforce protected routes by requiring token verification?

easy

A. BackgroundTasks

B. Depends

C. Query

D. Path

Solution

1. Step 1: Recall FastAPI dependency injection

   FastAPI uses Depends to declare dependencies like authentication checks.

2. Step 2: Match feature to protected routes

   Using Depends with a function that verifies tokens enforces protection on routes.

3. Final Answer:

   Depends -> Option B

4. Quick Check:

   Token check uses Depends [OK]

Hint: Use Depends to add token checks on routes [OK]

Common Mistakes:

• Confusing Depends with query or path parameters
• Using BackgroundTasks for authentication
• Not using any dependency for protection

3. Given this FastAPI code snippet, what will happen when accessing /users/me without a token?

from fastapi import FastAPI, Depends, HTTPException
from fastapi.security import OAuth2PasswordBearer

app = FastAPI()
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

def get_current_user(token: str = Depends(oauth2_scheme)):
    if token != "validtoken":
        raise HTTPException(status_code=401, detail="Invalid token")
    return {"username": "user1"}

@app.get("/users/me")
async def read_users_me(current_user: dict = Depends(get_current_user)):
    return current_user

medium

A. Raises HTTP 401 Unauthorized error

B. Returns {"username": "user1"} regardless of token

C. Returns an empty response

D. Raises HTTP 404 Not Found error

Solution

1. Step 1: Analyze token dependency behavior

   The function get_current_user checks if the token equals "validtoken"; otherwise, it raises HTTP 401.

2. Step 2: Consider no token case

   Without a token, oauth2_scheme will not provide a valid token, so the check fails and raises HTTP 401.

3. Final Answer:

   Raises HTTP 401 Unauthorized error -> Option A

4. Quick Check:

   No token = HTTP 401 error [OK]

Hint: No valid token triggers HTTP 401 error [OK]

Common Mistakes:

• Assuming it returns user data without token
• Confusing 401 with 404 error
• Expecting empty response instead of error

4. Identify the error in this FastAPI protected route code:

from fastapi import FastAPI, Depends, HTTPException
from fastapi.security import OAuth2PasswordBearer

app = FastAPI()
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

def get_current_user(token: str):
    if token != "secret":
        raise HTTPException(status_code=401, detail="Unauthorized")
    return {"user": "admin"}

@app.get("/dashboard")
async def dashboard(user: dict = Depends(get_current_user)):
    return user

medium

A. OAuth2PasswordBearer is not imported

B. HTTPException is not imported

C. Missing Depends in get_current_user parameter

D. Route path is invalid

Solution

1. Step 1: Check get_current_user parameter

   The function expects token: str but does not use Depends(oauth2_scheme) to get the token automatically.

2. Step 2: Identify missing dependency injection

   Without Depends(oauth2_scheme), FastAPI won't provide the token, causing an error.

3. Final Answer:

   Missing Depends in get_current_user parameter -> Option C

4. Quick Check:

   Token param needs Depends(oauth2_scheme) [OK]

Hint: Use Depends(oauth2_scheme) to get token in dependencies [OK]

Common Mistakes:

• Forgetting to import HTTPException
• Not using Depends for token parameter
• Incorrect route path syntax

5. How can you combine FastAPI's OAuth2PasswordBearer with a custom user verification function to protect multiple routes efficiently?

hard

A. Create a reusable dependency function that uses OAuth2PasswordBearer to get the token and verifies the user, then use Depends on routes

B. Add token verification code inside each route handler separately

C. Use OAuth2PasswordBearer only in the main app instance without dependencies

D. Skip token verification and rely on client-side checks

Solution

1. Step 1: Understand reusable dependency pattern

   Creating a function that uses OAuth2PasswordBearer to get the token and verifies the user allows reuse across routes.

2. Step 2: Apply Depends to routes

   Using Depends with this function on multiple routes enforces protection without repeating code.

3. Final Answer:

   Create a reusable dependency function that uses OAuth2PasswordBearer to get the token and verifies the user, then use Depends on routes -> Option A

4. Quick Check:

   Reusable dependency + Depends = efficient protection [OK]

Hint: Make one verify function and reuse with Depends on routes [OK]

Common Mistakes:

• Duplicating token checks in every route
• Not using Depends for token verification
• Ignoring server-side token checks