Function request_cleartext_password 

async fn request_cleartext_password<A>(
    conn: &mut FramedConn<A>,
) -> Result<String, PasswordRequestError>
where
    A: AsyncRead + AsyncWrite + AsyncReady + Send + Sync + Unpin,

Requests a cleartext password from a connection and returns it if it is valid. Sends an error response in the connection if the password is not valid.