import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.commons.codec.digest.HmacUtils;
String sign(Map<String, String> payload, String secret) {
ObjectMapper mapper = new ObjectMapper();
String str = mapper.writeValueAsString(payload);
return new HmacUtils(HmacAlgorithms.HMAC_SHA_256, secret).hmacHex(str);