static byte[] rsaSignDigestWithPrivateKey(PrivateKey javaKey, int openSSLPadding,
            byte[] message) {
        // An RSA cipher + ENCRYPT_MODE produces a standard RSA signature
        return rsaOpWithPrivateKey(javaKey, openSSLPadding, Cipher.ENCRYPT_MODE, message);
    }
Finds providers that are not us that provide the requested algorithms.
common/src/main/java/org/conscrypt/CryptoUpcalls.java