OAuth2\OAuth2::grantAccessTokenExtension PHP Method

    protected function grantAccessTokenExtension(IOAuth2Client $client, array $inputData, array $authHeaders)
    {
        if (!$this->storage instanceof IOAuth2GrantExtension) {
            throw new OAuth2ServerException(self::HTTP_BAD_REQUEST, self::ERROR_UNSUPPORTED_GRANT_TYPE);
        }
        $uri = $inputData["grant_type"];
        if (substr($uri, 0, 4) !== 'urn:') {
            $uri = filter_var($uri, FILTER_VALIDATE_URL);
        }
        $stored = $this->storage->checkGrantExtension($client, $uri, $inputData, $authHeaders);
        if ($stored === false) {
            throw new OAuth2ServerException(self::HTTP_BAD_REQUEST, self::ERROR_INVALID_GRANT);
        }
        return $stored;
    }