static String getServerX509KeyType(long sslCipherNative) {
        String kx_name = NativeCrypto.SSL_CIPHER_get_kx_name(sslCipherNative);
        if (kx_name.equals("RSA") || kx_name.equals("DHE_RSA") || kx_name.equals("ECDHE_RSA")) {
            return KEY_TYPE_RSA;
        } else if (kx_name.equals("ECDHE_ECDSA")) {
            return KEY_TYPE_EC;
        } else {
            return null;
        }
    }
Returns key type constant suitable for calling X509KeyManager.chooseServerAlias or
X509ExtendedKeyManager.chooseEngineServerAlias. Returns {@code null} for key exchanges that
do not use X.509 for server authentication.
common/src/main/java/org/conscrypt/SSLUtils.java