Role-based access control 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

CHTTPException

DDepends

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request instead of FastAPI

Trying to create app without importing FastAPI

The FastAPI class is imported from the fastapi module to create the app instance.

2fill in blank

medium

Complete the code to define a dependency that checks user roles.

FastAPI

from fastapi import Depends, HTTPException

def get_current_user(role: str):
    def role_checker(user=Depends(get_user)):
        if user.role != [1]:
            raise HTTPException(status_code=403, detail="Forbidden")
        return user
    return role_checker

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

Aguest

Badmin

Cuser

Dmoderator

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong role string

Not raising HTTPException on role mismatch

The role_checker checks if the user's role matches the required role, here 'admin'.

3fill in blank

hard

Fix the error in the route dependency injection for role-based access.

FastAPI

@app.get("/admin")
async def admin_panel(user=Depends([1]("admin"))):
    return {"message": f"Welcome {user.name} to admin panel"}

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

Aget_user

BDepends

Cget_current_user

DHTTPException

Attempts:

3 left

💡 Hint

Common Mistakes

Using Depends directly instead of the role-checking function

Using get_user which does not check roles

The route depends on the get_current_user function with the role 'admin' to enforce access control.

4fill in blank

hard

Fill both blanks to create a route that allows only moderators to access.

FastAPI

@app.get("/moderator")
async def mod_panel(user=Depends([1]([2]))):
    return {"message": f"Hello {user.name}, you are a moderator"}

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

Aget_current_user

B"moderator"

C"admin"

Dget_user

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 'admin' instead of 'moderator'

Using get_user which does not enforce roles

The route uses get_current_user with the role 'moderator' to restrict access.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension filtering users by role.

FastAPI

users = [
    {"name": "Alice", "role": "admin"},
    {"name": "Bob", "role": "user"},
    {"name": "Carol", "role": "moderator"}
]
admin_users = {user[[1]]: user for user in users if user[[2]] == [3]

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

A"name"

B"role"

C"admin"

D"user"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'role' as key instead of 'name'

Filtering by wrong role string

The comprehension creates a dictionary of users whose role is 'admin', using their name as the key.

Practice

1. What is the main purpose of role-based access control (RBAC) in FastAPI?

easy

A. To speed up API response times

B. To limit user actions based on their assigned roles

C. To automatically generate API documentation

D. To handle database migrations

Solution

1. Step 1: Understand RBAC concept

   RBAC restricts what users can do depending on their roles, like admin or user.

2. Step 2: Identify RBAC purpose in FastAPI

   FastAPI uses RBAC to check user roles before allowing access to certain endpoints.

3. Final Answer:

   To limit user actions based on their assigned roles -> Option B

4. Quick Check:

   RBAC = limit actions by roles [OK]

Hint: RBAC controls user permissions by roles, not speed or docs [OK]

Common Mistakes:

• Confusing RBAC with performance optimization
• Thinking RBAC auto-generates docs
• Assuming RBAC manages database tasks

2. Which of the following is the correct way to declare a dependency that checks for an admin role in FastAPI?

easy

A. def admin_required(user: User = Depends(get_current_user)):
if user.role == 'guest':
raise HTTPException(status_code=401)

B. def admin_required(user: User):
if user.role == 'admin':
return True

C. def admin_required():
return 'admin' in user.roles

D. def admin_required(user: User = Depends(get_current_user)):
if user.role != 'admin':
raise HTTPException(status_code=403)

Solution

1. Step 1: Check dependency signature

   def admin_required(user: User = Depends(get_current_user)): if user.role != 'admin': raise HTTPException(status_code=403) uses Depends to get current user, which is required for role checking.

2. Step 2: Verify role check logic

   def admin_required(user: User = Depends(get_current_user)): if user.role != 'admin': raise HTTPException(status_code=403) raises HTTP 403 if user is not admin, correctly enforcing access control.

3. Final Answer:

   def admin_required(user: User = Depends(get_current_user)): if user.role != 'admin': raise HTTPException(status_code=403) -> Option D

4. Quick Check:

   Depends + role check + HTTPException = def admin_required(user: User = Depends(get_current_user)): if user.role != 'admin': raise HTTPException(status_code=403) [OK]

Hint: Use Depends to get user, then check role and raise HTTPException [OK]

Common Mistakes:

• Not using Depends to get current user
• Checking wrong role or missing exception
• Returning True instead of raising exception

3. Given this FastAPI endpoint with role check dependency:

async def get_admin_data(admin: None = Depends(admin_required)):
    return {"data": "secret"}

What happens if a user with role 'user' calls this endpoint?

medium

A. The endpoint raises HTTP 403 Forbidden error

B. The endpoint returns {"data": "secret"}

C. The endpoint raises HTTP 401 Unauthorized error

D. The endpoint returns an empty response

Solution

1. Step 1: Understand admin_required behavior

   admin_required raises HTTP 403 if user role is not 'admin'.

2. Step 2: Apply to user role 'user'

   User role 'user' is not 'admin', so HTTP 403 is raised before endpoint runs.

3. Final Answer:

   The endpoint raises HTTP 403 Forbidden error -> Option A

4. Quick Check:

   Non-admin user triggers 403 error [OK]

Hint: Non-admin roles cause 403 error before endpoint runs [OK]

Common Mistakes:

• Confusing 401 Unauthorized with 403 Forbidden
• Expecting endpoint to return data for non-admin
• Thinking empty response is returned

4. Identify the error in this FastAPI role check dependency:

def check_admin(user: User = Depends(get_current_user)):
    if user.role == 'admin':
        return True
    else:
        return False

@app.get('/admin')
async def admin_panel(is_admin: bool = Depends(check_admin)):
    if not is_admin:
        raise HTTPException(status_code=403)
    return {"msg": "Welcome admin"}

medium

A. Dependency should raise HTTPException directly, not return bool

B. Depends should not be used inside dependency functions

C. The endpoint should not check is_admin, dependency handles it

D. The function should return user object, not bool

Solution

1. Step 1: Analyze dependency behavior

   check_admin returns True/False instead of raising HTTPException on failure.

2. Step 2: Understand best practice for RBAC in FastAPI

   Dependencies should raise HTTPException to stop execution early, not return bool flags.

3. Final Answer:

   Dependency should raise HTTPException directly, not return bool -> Option A

4. Quick Check:

   Raise exception in dependency, don't return bool [OK]

Hint: Raise HTTPException in dependency to block access immediately [OK]

Common Mistakes:

• Returning bool instead of raising exception
• Not stopping request early in dependency
• Misusing Depends inside dependencies

5. You want to create a reusable role checker in FastAPI that allows multiple roles (e.g., 'admin' or 'moderator') to access an endpoint. Which approach correctly implements this?

hard

A. def role_checker(user: User = Depends(get_current_user)):
if user.role == 'admin' and user.role == 'moderator':
return True
raise HTTPException(status_code=403)

B. def role_checker(user: User = Depends(get_current_user)):
if user.role != 'admin' or user.role != 'moderator':
raise HTTPException(status_code=403)

C. def role_checker(allowed_roles: list[str]):
def checker(user: User = Depends(get_current_user)):
if user.role not in allowed_roles:
raise HTTPException(status_code=403)
return checker

D. def role_checker(allowed_roles: list[str]):
for role in allowed_roles:
if role == user.role:
return True
return False

Solution

1. Step 1: Understand reusable dependency pattern

   def role_checker(allowed_roles: list[str]): def checker(user: User = Depends(get_current_user)): if user.role not in allowed_roles: raise HTTPException(status_code=403) return checker returns a function that checks if user role is in allowed_roles, raising HTTPException if not.

2. Step 2: Verify logic for multiple roles

   def role_checker(allowed_roles: list[str]): def checker(user: User = Depends(get_current_user)): if user.role not in allowed_roles: raise HTTPException(status_code=403) return checker correctly uses 'not in' to allow any role in the list, making it reusable.

3. Final Answer:

   def role_checker(allowed_roles: list[str]): def checker(user: User = Depends(get_current_user)): if user.role not in allowed_roles: raise HTTPException(status_code=403) return checker -> Option C

4. Quick Check:

   Reusable role check with allowed_roles list = def role_checker(allowed_roles: list[str]): def checker(user: User = Depends(get_current_user)): if user.role not in allowed_roles: raise HTTPException(status_code=403) return checker [OK]

Hint: Return inner function checking role in allowed_roles, raise HTTPException [OK]

Common Mistakes:

• Using incorrect logic with 'or' instead of 'in'
• Returning bool instead of raising exception
• Checking impossible conditions like role == 'admin' and 'moderator'