Some fixes

lib/helpers/api_helper.dart

@@ -23,7 +23,7 @@ class ApiHelper {
     final state = data["state"] ?? "";
 
     if (userId == null || accessToken == null || redirectUri == null) {
-      return Response(400, body: "Missing parameters");
+      return Response(400, body: json.encode({"error": "Missing parameters"}));
     }
 
     final settings = ref.read(SettingsController.provider)!;
@@ -33,7 +33,9 @@ class ApiHelper {
     );
 
     if (whoamiRes.statusCode != 200) {
-      return Response.forbidden("Access token validation failed");
+      return Response.forbidden(
+        json.encode({"error": "Access token validation failed"}),
+      );
     }
 
     final code = base64Url.encode(
@@ -71,7 +73,10 @@ class ApiHelper {
     final redirectUri = query["redirect_uri"];
 
     if (code == null || redirectUri == null) {
-      return Response(400, body: "Missing code or redirect_uri");
+      return Response(
+        400,
+        body: json.encode({"error": "Missing code or redirect_uri"}),
+      );
     }
 
     final tokenRes = await tokenHandler(
@@ -83,7 +88,7 @@ class ApiHelper {
     );
 
     if (tokenRes.statusCode != 200) {
-      return Response(400, body: "Token post failed");
+      return Response(400, body: json.encode({"error": "Token post failed"}));
     }
 
     return Response.found(
@@ -102,12 +107,15 @@ class ApiHelper {
     final clientId = body["client_id"];
 
     if (code == null || clientId == null) {
-      return Response(400, body: "Missing code or client_id");
+      return Response(
+        400,
+        body: json.encode({"error": "Missing code or client_id"}),
+      );
     }
 
     final codes = ref.read(AuthCodeController.provider);
     if (!codes.containsKey(code)) {
-      return Response(400, body: "Invalid code");
+      return Response(400, body: json.encode({"error": "Invalid code"}));
     }
 
     final user = codes[code]!;
@@ -173,7 +181,9 @@ class ApiHelper {
 
   Future<Response> introspectionHandler(Request request) async {
     final token = Uri.splitQueryString(await request.readAsString())["token"];
-    if (token == null) return Response(400, body: "Missing token");
+    if (token == null) {
+      return Response(400, body: json.encode({"error": "Missing token"}));
+    }
 
     try {
       JWT.verify(
@@ -213,7 +223,7 @@ class ApiHelper {
   }
 
   Future<Response> logoutHandler(Request request) async =>
-      Response.ok("Log out is not currently implemented");
+      Response.ok(json.encode("Log out is not currently implemented"));
 
   Response openidConfiguration(_) {
     final settings = ref.read(SettingsController.provider)!;