Improve html error detection

In case the header is not correctly set, try to detect html error messages
from the content itself

lib/core/exceptions/http_exception.dart

@@ -1,6 +1,6 @@
 /*
  * This file is part of wger Workout Manager <https://github.com/wger-project>.
- * Copyright (c) 2020 - 2025 wger Team
+ * Copyright (c) 2020 - 2026 wger Team
  *
  * wger Workout Manager is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as published by
@@ -43,7 +43,8 @@ class WgerHttpException implements Exception {
     final dynamic responseBody = response.body;
 
     final contentType = response.headers[HttpHeaders.contentTypeHeader];
-    if (contentType != null && contentType.contains('text/html')) {
+    if ((contentType != null && contentType.contains('text/html')) ||
+        responseBody.toString().contains('<html')) {
       type = ErrorType.html;
     }
 

lib/helpers/errors.dart

@@ -1,6 +1,6 @@
 /*
  * This file is part of wger Workout Manager <https://github.com/wger-project>.
- * Copyright (c) 2020 - 2025 wger Team
+ * Copyright (c) 2020 - 2026 wger Team
  *
  * wger Workout Manager is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as published by
@@ -51,8 +51,6 @@ void showHttpExceptionErrorDialog(WgerHttpException exception, {BuildContext? co
     return;
   }
 
-  final theme = Theme.of(dialogContext);
-
   showDialog(
     context: dialogContext,
     builder: (ctx) => AlertDialog(

lib/providers/auth.dart

@@ -1,6 +1,6 @@
 /*
  * This file is part of wger Workout Manager <https://github.com/wger-project>.
- * Copyright (c) 2020 - 2025 wger Team
+ * Copyright (c) 2020 - 2026 wger Team
  *
  * wger Workout Manager is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as published by
@@ -58,7 +58,7 @@ class AuthProvider with ChangeNotifier {
   static const SERVER_VERSION_URL = 'version';
   static const REGISTRATION_URL = 'register';
   static const LOGIN_URL = 'login';
-  static const TEST_URL = 'userprofile';
+  static const USERPROFILE_URL = 'userprofile';
 
   late http.Client client;
 
@@ -150,7 +150,7 @@ class AuthProvider with ChangeNotifier {
     // Login using the API token
     if (apiToken != null && apiToken.isNotEmpty) {
       final response = await client.get(
-        makeUri(serverUrl, TEST_URL),
+        makeUri(serverUrl, USERPROFILE_URL),
         headers: {
           HttpHeaders.contentTypeHeader: 'application/json; charset=UTF-8',
           HttpHeaders.userAgentHeader: getAppNameHeader(),

test/core/http_exception_test.dart

@@ -1,6 +1,6 @@
 /*
  * This file is part of wger Workout Manager <https://github.com/wger-project>.
- * Copyright (c) 2020 - 2025 wger Team
+ * Copyright (c) 2020 - 2026 wger Team
  *
  * wger Workout Manager is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as published by
@@ -25,20 +25,24 @@ import 'package:wger/core/exceptions/http_exception.dart';
 void main() {
   group('WgerHttpException', () {
     test('parses valid JSON response', () {
+      // Arrange
       final resp = http.Response(
         '{"foo":"bar"}',
         400,
         headers: {HttpHeaders.contentTypeHeader: 'application/json'},
       );
 
+      // Act
       final ex = WgerHttpException(resp);
 
+      // Assert
       expect(ex.type, ErrorType.json);
       expect(ex.errors['foo'], 'bar');
       expect(ex.toString(), contains('WgerHttpException'));
     });
 
     test('falls back on malformed JSON', () {
+      // Arrange
       const body = '{"foo":';
       final resp = http.Response(
         body,
@@ -46,13 +50,16 @@ void main() {
         headers: {HttpHeaders.contentTypeHeader: 'application/json'},
       );
 
+      // Act
       final ex = WgerHttpException(resp);
 
+      // Assert
       expect(ex.type, ErrorType.json);
       expect(ex.errors['unknown_error'], body);
     });
 
-    test('detects HTML response', () {
+    test('detects HTML response from headers', () {
+      // Arrange
       const body = '<html lang="en"><body>Error</body></html>';
       final resp = http.Response(
         body,
@@ -60,16 +67,39 @@ void main() {
         headers: {HttpHeaders.contentTypeHeader: 'text/html; charset=utf-8'},
       );
 
+      // Act
       final ex = WgerHttpException(resp);
 
+      // Assert
+      expect(ex.type, ErrorType.html);
+      expect(ex.htmlError, body);
+    });
+
+    test('detects HTML response from content', () {
+      // Arrange
+      const body = '<html lang="en"><body>Error</body></html>';
+      final resp = http.Response(
+        body,
+        500,
+        headers: {HttpHeaders.contentTypeHeader: 'text/foo; charset=utf-8'},
+      );
+
+      // Act
+      final ex = WgerHttpException(resp);
+
+      // Assert
       expect(ex.type, ErrorType.html);
       expect(ex.htmlError, body);
     });
 
     test('fromMap sets errors and type', () {
+      // Arrange
       final map = <String, dynamic>{'field': 'value'};
+
+      // Act
       final ex = WgerHttpException.fromMap(map);
 
+      // Assert
       expect(ex.type, ErrorType.json);
       expect(ex.errors, map);
     });