fixed missing payload encoding conversion

lib/src/front-token.dart

@@ -31,7 +31,7 @@ class FrontToken {
 
   static Map<String, dynamic> _parseFrontToken(fronTokenDecoded) {
     var base64Decoded = base64Decode(fronTokenDecoded);
-    String decodedString = new String.fromCharCodes(base64Decoded);
+    String decodedString = utf8.decode(base64Decoded);
     var result = jsonDecode(decodedString);
     return result;
   }

test/accesstoken_http_test.dart

@@ -65,6 +65,23 @@ void main() {
     }
   });
 
+  test("should convert utf-8 access token payload to utf-16", () async {
+    await SuperTokensTestUtils.startST(validity: 3);
+    SuperTokens.init(apiDomain: apiBasePath);
+    Request req = SuperTokensTestUtils.getLoginRequestUtf8Encoded();
+    StreamedResponse streamedResp;
+    streamedResp = await http.send(req);
+    var resp = await Response.fromStream(streamedResp);
+    if (resp.statusCode != 200) {
+      fail("login failed");
+    }
+
+    var payload = await SuperTokens.getAccessTokenPayloadSecurely();
+    assert(payload.length == 1);
+    assert(payload["name"] == "öäü-áàâ");
+    assert(payload["name"] == "\u00f6\u00e4\u00fc\u002d\u00e1\u00e0\u00e2");
+  });
+
   test("should be able to refresh a session started w/ CDI 2.18", () async {
     await SuperTokensTestUtils.startST(validity: 3);
     SuperTokens.init(apiDomain: apiBasePath);

test/test-utils.dart

@@ -68,6 +68,18 @@ class SuperTokensTestUtils {
     return request;
   }
 
+  static http.Request getLoginRequestUtf8Encoded() {
+    var loginAPIURL = "$baseUrl/login";
+    var request = http.Request('POST', Uri.parse(loginAPIURL));
+    request.headers['Content-Type'] = "application/json; charset=utf-8";
+    var body = {"userId": "supertokens-flutter-tests", "payload": {
+      "name": "\xc3\xb6\xc3\xa4\xc3\xbc\x2d\xc3\xa1\xc3\xa0\xc3\xa2" // UTF-8 encoded öäü-áàâ
+    }};
+    var jsonBody = jsonEncode(body);
+    request.body = jsonBody;
+    return request;
+  }
+
   static http.Request getLogin218Request() {
     var loginAPIURL = "$baseUrl/login-2.18";
     var request = http.Request('POST', Uri.parse(loginAPIURL));