Function finalize_session 

pub async fn finalize_session<'store>(
    response: Response,
    response_cookies: &mut ResponseCookies,
    processor: &Processor,
    session: Session<'store>,
) -> Result<Response, FinalizeError>

A post-processing middleware to attach a session cookie to the outgoing response, if needed.

It will also sync the session server-side state with the chosen storage backend.