ParagonIE\EasyRSA\EasyRSA::sign PHP Method

    public static function sign($message, PrivateKey $rsaPrivateKey)
    {
        static $rsa = null;
        if (!$rsa) {
            $rsa = new RSA();
            $rsa->setSignatureMode(RSA::SIGNATURE_PSS);
            $rsa->setMGFHash('sha256');
        }
        $rsa->loadKey($rsaPrivateKey->getKey());
        return $rsa->sign($message);
    }

 public function testSign()
 {
     $keyPair = KeyPair::generateKeyPair(2048);
     $secretKey = $keyPair->getPrivateKey();
     $publicKey = $keyPair->getPublicKey();
     $plain = 'This is a message.';
     $signature = EasyRSA::sign($plain, $secretKey);
     $this->assertTrue(EasyRSA::verify($plain, $signature, $publicKey));
 }