protected void configureSigningKeyFromPrivateKeyResource(final String signingSecretKey) {
        val object = extractPrivateKeyFromResource(signingSecretKey);
        LOGGER.trace("Located signing key resource [{}]", signingSecretKey);
        setSigningKey(object);
    }
Sets signing key. If the key provided is resolved as a private key,
then will create use the private key as is, and will sign values
using RSA. Otherwise, AES is used.

@param signingSecretKey the signing secret key
core/cas-server-core-util-api/src/main/java/org/apereo/cas/util/cipher/AbstractCipherExecutor.java