private static X509KeyManager findFirstX509KeyManager(KeyManager[] kms) {
        for (KeyManager km : kms) {
            if (km instanceof X509KeyManager) {
                return (X509KeyManager)km;
            }
        }
        return null;
    }
Returns X.509 key manager or null for none.
common/src/main/java/org/conscrypt/SSLParametersImpl.java