signRequest static method
Computes an HMAC-SHA256 signature (as a lowercase hex string) over
payload, keyed with secret.
Implementation
static String signRequest(String secret, Map<String, dynamic> payload) {
final message = _canonicalize(payload);
final hmac = Hmac(sha256, utf8.encode(secret));
return hmac.convert(utf8.encode(message)).toString();
}