decryptToken method
Implementation
@override
FutureOr<String> decryptToken(AccessToken token) async {
var header = <String, dynamic>{"alg": "HS256", "typ": "JWT"};
var payload = token.toMap();
var base64Payload = base64Url.encode(utf8.encode(json.encode(payload)));
var base64Header = base64Url.encode(utf8.encode(json.encode(header)));
///
var cT = "$base64Header.$base64Payload";
///
var hash = await crypto.calculateSha256Mac(utf8.encode(cT));
return "$cT.${base64Url.encode(hash)}";
}