PayPal\Auth\Oauth\OAuthServer::get_token PHP Method

    private function get_token($request, $consumer, $token_type = "access")
    {
        $token_field = $request instanceof OAuthRequest ? $request->get_parameter('oauth_token') : null;
        $token = $this->data_store->lookup_token($consumer, $token_type, $token_field);
        if (!$token) {
            throw new OAuthException("Invalid {$token_type} token: {$token_field}");
        }
        return $token;
    }