Bearer token handling in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Bearer token in API authentication?

A Bearer token is a security token that a client sends to a server to prove its identity. It is called 'Bearer' because whoever holds the token can access the protected resource.

beginner

How does FastAPI extract a Bearer token from an HTTP request?

FastAPI uses the OAuth2PasswordBearer class to declare a dependency that extracts the Bearer token from the Authorization header automatically.

intermediate

Show a simple FastAPI dependency that reads a Bearer token from the Authorization header.

from fastapi import Depends
from fastapi.security import OAuth2PasswordBearer
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

async def get_token(token: str = Depends(oauth2_scheme)):
    return token

intermediate

Why should you validate the Bearer token after extracting it in FastAPI?

Extracting the token only gets the string. You must validate it to check if it is correct, not expired, and belongs to an authorized user before allowing access.

beginner

What HTTP header carries the Bearer token in a request?

The Authorization header carries the Bearer token, formatted as: Authorization: Bearer <token>

Which FastAPI class helps extract Bearer tokens from requests?

A Depends

B HTTPBearer

C APIKeyHeader

D OAuth2PasswordBearer

OAuth2PasswordBearer is designed to extract Bearer tokens from the Authorization header in FastAPI.

What prefix must the Authorization header contain for a Bearer token?

A Token

B Bearer

C Basic

D APIKey

Bearer tokens are sent with the prefix 'Bearer' in the Authorization header.

After extracting a Bearer token, what is the next important step?

A Validate the token's authenticity and expiry

B Send it back to the client

C Store it in a database

D Ignore it

Validation ensures the token is valid and the user is authorized.

In FastAPI, how do you declare a dependency to get the Bearer token?

A Use Depends with APIKeyQuery

B Use Depends with HTTPBasic

C Use Depends with OAuth2PasswordBearer instance

D Use Depends with Cookie

OAuth2PasswordBearer is used with Depends to extract Bearer tokens.

What HTTP status code should you return if the Bearer token is missing or invalid?

A 401 Unauthorized

B 200 OK

C 403 Forbidden

D 404 Not Found

401 Unauthorized indicates the client must authenticate with a valid token.

Explain how FastAPI handles Bearer token extraction and validation in a simple API endpoint.

Think about the Authorization header and FastAPI's dependency system.

Describe the role of the Authorization header and the Bearer token format in API security.

Focus on how the token is sent and why it matters.