encryptToken method
Implementation
Future<String> encryptToken(Map<String, dynamic> payload) async {
var h = {"alg": "HS512", "typ": "JWT"};
var base64H = base64.encode(utf8.encode(json.encode(h)));
var base64P = base64.encode(utf8.encode(json.encode(payload)));
var macMessage = base64.encode(utf8.encode("$base64H.$base64P"));
var alg = AesCtr.with256bits(macAlgorithm: Hmac.sha512());
var mac = await alg.encrypt(utf8.encode(macMessage),
secretKey: SecretKey(__tokenSecretKey1.codeUnits));
return "$base64H.$base64P.${mac.cipherText}";
}