fix(auth): configurable SameSite cookie for cross-origin dev setup

Chrome 89+ schemeful same-site treats http://localhost and https://localhost
as different sites, blocking SameSite=Strict cookies on cross-origin fetch
(e.g. Vite on port 5173, API on port 7221).

Fix: make CookieSameSite configurable per environment in JwtSettings.
- Default: Strict (production)
- appsettings.Development.json: None (allows cross-origin cookie in dev)
- When SameSite=None, Secure is always forced (browser requirement)

Revert the earlier Vite proxy approach in favour of this backend config.
VITE_API_BASE_URL remains a freely configurable URL in .env.local.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/SlpModularCms.Api/appsettings.Development.json

@@ -13,7 +13,8 @@
     "Issuer": "SlpModularCms",
     "Audience": "SlpModularCmsPortal",
     "ExpiryMinutes": 60,
-    "RefreshTokenExpiryDays": 7
+    "RefreshTokenExpiryDays": 7,
+    "CookieSameSite": "None"
   },
   "Availability": {
     "CircuitBreakerSeconds": 30,

src/SlpModularCms.Core/Identity/Models/JwtSettings.cs

@@ -10,4 +10,10 @@ public class JwtSettings
     public string Audience { get; set; } = string.Empty;
     public int ExpiryMinutes { get; set; } = 60;
     public int RefreshTokenExpiryDays { get; set; } = 7;
+    /// <summary>
+    /// SameSite-modus voor de refreshToken cookie: Strict | Lax | None.
+    /// Gebruik None in ontwikkelomgevingen waar frontend en backend
+    /// op verschillende poorten draaien (vereist Secure=true).
+    /// </summary>
+    public string CookieSameSite { get; set; } = "Strict";
 }

src/SlpModularCms.Modules.Identity/Controllers/AuthController.cs

@@ -2,6 +2,7 @@ using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.RateLimiting;
+using Microsoft.Extensions.Options;
 using SlpModularCms.Core.Identity.Models;
 using SlpModularCms.Core.Identity.Services;
 
@@ -12,10 +13,12 @@ namespace SlpModularCms.Modules.Identity.Controllers;
 public class AuthController : ControllerBase
 {
     private readonly IAuthService _authService;
+    private readonly JwtSettings _jwtSettings;
 
-    public AuthController(IAuthService authService)
+    public AuthController(IAuthService authService, IOptions<JwtSettings> jwtSettings)
     {
         _authService = authService;
+        _jwtSettings = jwtSettings.Value;
     }
 
     [HttpPost("login")]
@@ -65,11 +68,15 @@ public class AuthController : ControllerBase
 
     private CookieOptions GetCookieOptions()
     {
+        var sameSite = Enum.TryParse<SameSiteMode>(_jwtSettings.CookieSameSite, ignoreCase: true, out var parsed)
+            ? parsed
+            : SameSiteMode.Strict;
+
         return new CookieOptions
         {
             HttpOnly = true,
-            Secure = Request.IsHttps,
-            SameSite = SameSiteMode.Strict,
+            Secure = Request.IsHttps || sameSite == SameSiteMode.None,
+            SameSite = sameSite,
             Path = "/api/v1/auth",
             Expires = DateTimeOffset.UtcNow.AddDays(7)
         };