Signature algorithm generation rules

When requesting MultiExchange OpenAPI, you need to combine "appId" and "timestamp" to generate "content (appId=?×tamp=?)" and a signature as shown in the following example.

private String genSignature(String payload, String timestamp) throws GeneralSecurityException {
        StringBuilder builder = new StringBuilder();
        if (StringUtils.isNotBlank(payload)) {
            builder.append(payload).append("&");
        }

        builder.append(HEADER_MERCHANT_CODE).append('=').append(this.plutoConfig.getMerchantCode()).append('&')
                .append(HEADER_TIMESTAMP).append('=').append(timestamp);
//        LogUtils.maskInfo("original request content:{}", builder.toString());
        // do sign.
        String pk = ChannelClientApolloUtils.getKmsMerchantPrivateKey();
        if (StringUtils.isEmpty(pk)) {
            throw new GeneralSecurityException("no merchant private key.");
        }
        return RsaUtil.sign(pk, builder.toString());
    }

/**
@param privateKey Provided by Multiexc, held by the merchant
@param content
**/
public static String sign(String privateKey, String content) throws GeneralSecurityException {
    byte[] bytes = Base64.getDecoder().decode(privateKey.getBytes());
    PrivateKey pk = generatePrivateKey(bytes);
    pk = generatePrivateKey(pk.getEncoded());

    Signature signature = Signature.getInstance("SHA256withRSA");
    signature.initSign(pk);
    signature.update(content.getBytes());
    return new String(Base64.getEncoder().encode(signature.sign()));
}

private static PrivateKey generatePrivateKey(byte[] bytes) throws GeneralSecurityException {
    PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(bytes);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    return keyFactory.generatePrivate(keySpec);
}

/**
 * verify signature
 *
 * @param sourceData
 * @param publicKey
 * @param sign
 * @return
 * @throws Exception
 */
public static boolean verify(String sourceData, PublicKey publicKey, String sign) throws Exception {
    byte[] keyBytes = publicKey.getEncoded();
    X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    PublicKey key = keyFactory.generatePublic(keySpec);
    Signature signature = Signature.getInstance("SHA256withRSA");
    signature.initVerify(key);
    signature.update(sourceData.getBytes());
    return signature.verify(Base64.decodeBase64(sign.getBytes()));
}