How to Decode Basic Auth Credentials in Python

import base64

def decode_basic_auth(header_value):
    """
    Decode credentials from a Basic Auth header value.
    
    Expected format: "Basic base64encoded(username:password)"
    Returns a tuple (username, password).
    """
    if not header_value.startswith("Basic "):
        raise ValueError("Invalid Basic Auth header format")
    
    encoded_part = header_value.split(" ", 1)[1]
    decoded_bytes = base64.b64decode(encoded_part)
    decoded_str = decoded_bytes.decode("utf-8")
    
    if ":" not in decoded_str:
        raise ValueError("Decoded credentials missing ':' separator")
    
    username, password = decoded_str.split(":", 1)
    return username, password

if __name__ == "__main__":
    # Mock test credentials
    test_username = "admin"
    test_password = "secret123"
    
    # Encode for the mock header
    raw_credentials = f"{test_username}:{test_password}"
    encoded_credentials = base64.b64encode(raw_credentials.encode("utf-8")).decode("utf-8")
    mock_header = f"Basic {encoded_credentials}"
    
    print(f"Mock header: {mock_header}")
    
    # Decode and display
    username, password = decode_basic_auth(mock_header)
    print(f"Decoded username: {username}")
    print(f"Decoded password: {password}")