Add player onboarding and tactical viewer updates

apps/backend/Auth/Simulation/HttpContextPlayerIdentityResolver.cs

@@ -5,6 +5,8 @@ namespace SpaceGame.Api.Auth.Simulation;
 
 public sealed class HttpContextPlayerIdentityResolver(IHttpContextAccessor httpContextAccessor) : IPlayerIdentityResolver
 {
+    public const string EffectivePlayerHeaderName = "X-Act-As-Player-Id";
+
     public Guid? GetCurrentPlayerId()
     {
         var subject = httpContextAccessor.HttpContext?.User.FindFirstValue(ClaimTypes.NameIdentifier)
@@ -15,6 +17,21 @@ public sealed class HttpContextPlayerIdentityResolver(IHttpContextAccessor httpC
     public Guid GetRequiredPlayerId() =>
       GetCurrentPlayerId() ?? throw new InvalidOperationException("Authenticated player identity is required.");
 
+    public Guid? GetEffectivePlayerId()
+    {
+        var currentPlayerId = GetCurrentPlayerId();
+        if (!CanAccessGm())
+        {
+            return currentPlayerId;
+        }
+
+        var requestedIdentity = httpContextAccessor.HttpContext?.Request.Headers[EffectivePlayerHeaderName].FirstOrDefault();
+        return Guid.TryParse(requestedIdentity, out var effectivePlayerId) ? effectivePlayerId : currentPlayerId;
+    }
+
+    public Guid GetRequiredEffectivePlayerId() =>
+      GetEffectivePlayerId() ?? throw new InvalidOperationException("Authenticated player identity is required.");
+
     public bool CanAccessGm()
     {
         var user = httpContextAccessor.HttpContext?.User;