Verify an id_token. This method will verify the current id_token, if one
isn't provided.

@throws LogicException If no token was provided and no token was set using `setAccessToken`.
@throws UnexpectedValueException If the token is not a valid JWT.
@param string|null $idToken The token (id_token) that should be verified.
@return array|false Returns the token payload as an array if the verification was
successful, false otherwise.