App\Http\Controllers\BotController::validateToken PHP Method

    private function validateToken($token)
    {
        if (!$token) {
            return false;
        }
        $token = explode(' ', $token)[1];
        // https://blogs.msdn.microsoft.com/tsmatsuz/2016/07/12/developing-skype-bot/
        // 0:Invalid, 1:Valid
        $token_valid = 0;
        // 1 separate token by dot (.)
        $token_arr = explode('.', $token);
        $headers_enc = $token_arr[0];
        $claims_enc = $token_arr[1];
        $sig_enc = $token_arr[2];
        // 2 base 64 url decoding
        $headers_arr = json_decode($this->base64_url_decode($headers_enc), TRUE);
        $claims_arr = json_decode($this->base64_url_decode($claims_enc), TRUE);
        $sig = $this->base64_url_decode($sig_enc);
        // 3 get key list
        $keylist = file_get_contents('https://api.aps.skype.com/v1/keys');
        $keylist_arr = json_decode($keylist, TRUE);
        foreach ($keylist_arr['keys'] as $key => $value) {
            // 4 select one key (which matches)
            if ($value['kid'] == $headers_arr['kid']) {
                // 5 get public key from key info
                $cert_txt = '-----BEGIN CERTIFICATE-----' . "\n" . chunk_split($value['x5c'][0], 64) . '-----END CERTIFICATE-----';
                $cert_obj = openssl_x509_read($cert_txt);
                $pkey_obj = openssl_pkey_get_public($cert_obj);
                $pkey_arr = openssl_pkey_get_details($pkey_obj);
                $pkey_txt = $pkey_arr['key'];
                // 6 verify signature
                $token_valid = openssl_verify($headers_enc . '.' . $claims_enc, $sig, $pkey_txt, OPENSSL_ALGO_SHA256);
            }
        }
        // 7 show result
        return $token_valid == 1;
    }