fix(backend/auth): Fix JWT token claim mapping for user ID

- Changed AuthService.GenerateJwtToken to use JWT standard claims:
  - JwtRegisteredClaimNames.Sub for user ID (instead of ClaimTypes.NameIdentifier)
  - JwtRegisteredClaimNames.Name for username
  - JwtRegisteredClaimNames.Email for email
  - JwtRegisteredClaimNames.UniqueName for additional username claim
  - Kept ClaimTypes.Role for role

- Updated AuthController.GetCurrentUser to use JwtRegisteredClaimNames.Sub
- Updated AdminController.DeleteUserAsync to use JwtRegisteredClaimNames.Sub

This fixes the 401 error when calling /me after login. The issue was that
tokens were being generated with ClaimTypes.NameIdentifier claim, but the
JWT middleware doesn't automatically map this to a claim that can be found
with User.FindFirst(). Using standard JWT claims (sub, name, email) ensures
proper compatibility with ASP.NET Core's JWT authentication.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

GermanApp/Infrastructure/Services/AuthService.cs

@@ -151,11 +151,14 @@ public class AuthService : IAuthService
         
         var credentials = new SigningCredentials(securityKey, SecurityAlgorithms.HmacSha256);
 
+        // Use JWT standard claims for better compatibility
+        // "sub" = subject (user identifier), "name" = username, "email" = email, "role" = user role
         var claims = new[]
         {
-            new Claim(ClaimTypes.NameIdentifier, user.Id.ToString()),
-            new Claim(ClaimTypes.Name, user.Username),
-            new Claim(ClaimTypes.Email, user.Email),
+            new Claim(JwtRegisteredClaimNames.Sub, user.Id.ToString()),  // JWT standard: sub for subject/user ID
+            new Claim(JwtRegisteredClaimNames.Name, user.Username),
+            new Claim(JwtRegisteredClaimNames.Email, user.Email),
+            new Claim(JwtRegisteredClaimNames.UniqueName, user.Username),  // Additional: unique name
             new Claim(ClaimTypes.Role, user.Role)  // Use user's actual role (User or Admin)
         };
 

GermanApp/Presentation/Controllers/AdminController.cs

@@ -4,7 +4,9 @@ using GermanApp.Application.DTOs.Auth;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
 using System.Collections.Generic;
+using System.IdentityModel.Tokens.Jwt;
 using System.Net;
+using System.Security.Claims;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -114,7 +116,11 @@ public class AdminController : ControllerBase
     {
         try
         {
-            var adminUserId = int.Parse(User.FindFirst("nameid")?.Value ?? "0");
+            // Get admin user ID from JWT "sub" claim (standard JWT claim for subject/user ID)
+            var adminUserIdClaim = User.FindFirst(JwtRegisteredClaimNames.Sub) ?? User.FindFirst("sub");
+            if (adminUserIdClaim == null || !int.TryParse(adminUserIdClaim.Value, out var adminUserId) || adminUserId == 0)
+                return Unauthorized();
+            
             var result = await _adminService.DeleteUserAsync(userId, adminUserId, cancellationToken);
             
             if (!result)

GermanApp/Presentation/Controllers/AuthController.cs

@@ -2,7 +2,9 @@ using GermanApp.Application.DTOs.Auth;
 using GermanApp.Application.Interfaces;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using System.IdentityModel.Tokens.Jwt;
 using System.Net;
+using System.Security.Claims;
 
 namespace GermanApp.Presentation.Controllers;
 
@@ -85,8 +87,9 @@ public class AuthController : ControllerBase
     {
         try
         {
-            var userId = int.Parse(User.FindFirst("nameid")?.Value ?? "0");
-            if (userId == 0)
+            // Get user ID from JWT "sub" claim (standard JWT claim for subject/user ID)
+            var userIdClaim = User.FindFirst(JwtRegisteredClaimNames.Sub) ?? User.FindFirst("sub");
+            if (userIdClaim == null || !int.TryParse(userIdClaim.Value, out var userId) || userId == 0)
                 return Unauthorized();
 
             var user = await _authService.GetCurrentUserAsync(userId);