Authentication

Documentation for get_current_user Function

Purpose:

The get_current_user function is designed to authenticate users by extracting and verifying a JWT (JSON Web Token) from the Authorization header in the incoming request. It is typically used to ensure that API calls are made by authenticated users.

Function Signature:

def get_current_user() -> Optional[str]:

Returns:

• Optional[str]: Returns the user ID if the token is successfully verified, otherwise returns None.

Detailed Behavior:

1. Authorization Header Check: The function first checks if the Authorization header is present in the request. If not, it returns None, indicating no user is authenticated.

2. Bearer Token Extraction: It then checks if the authorization scheme is Bearer, which is expected in the format “Bearer “. If the format is incorrect, it returns None.

3. Token Verification:

   • The token part is extracted from the header and passed to the verify_id_token function provided by Firebase Admin SDK.
   • This function verifies the token’s validity against Firebase’s authentication backend.
   • If the token is valid, the function extracts and returns the user’s UID from the decoded token.
   • If there is an exception during token verification (e.g., token is expired, invalid, or tampered), it catches the exception, logs the error, and returns None.

Usage:

This function is typically used in a web application’s backend routes to secure endpoints, ensuring that only requests from authenticated users are processed. It can be utilized in any route handler by calling get_current_user() to obtain the authenticated user’s ID.

Example:

from flask import jsonify

@app.route('/secure-data')
def secure_data():
    user_id = get_current_user()
    if not user_id:
        return jsonify({"error": "Unauthorized"}), 401
    # Proceed with handling the request knowing the user is authenticated
    return jsonify({"data": "Secure data accessible to authenticated users"})

Notes:

• This function assumes that the Firebase Admin SDK has been initialized in the application’s environment, which handles the actual token verification.
• The function uses Python’s optional type hint (Optional[str]) to indicate that the return value can be either a string (the user ID) or None.
• Proper error handling is crucial to avoid unauthorized access, so always check the return value of this function when authenticating users in your routes.