Return the currently-valid MFA token for this application.

def get_mfa(self):
        """Return the currently-valid MFA token for this application."""
        token = str(self.totp.now())
        # PyOTP doesn't pre-pad tokens shorter than 6 characters
        # ROTP does, so we have to.
        while len(token) < 6:
            token = '0{}'.format(token)
        return token