FastAPI Authentication | Dataford Interview Questions

FastAPI: how will you do authentication in FastAPI?

Asked in the round 1 stage.

Implement the framework-independent authentication dependency logic for a bearer token. Return the authenticated user details only when the Authorization header, token, expiration, and required scope are valid. Otherwise return None.

Input and Output

headers is a dictionary, token_store maps token strings to claim dictionaries, now is an integer timestamp, and required_scope is a string. Return {"user_id": ..., "scopes": [...]} for valid access, or None.

Constraints

Header names must be treated case-insensitively
The Authorization header must contain exactly two whitespace-separated fields
The authentication scheme must be Bearer, ignoring scheme casing
A token is valid only when expires_at > now
A valid token must contain the required scope

Function Signature

def authenticate_request(headers, token_store, now, required_scope):

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