Added validation and fixed errors

SchengenVisaApi/Infrastructure/Common/UserIdProvider.cs

@@ -0,0 +1,19 @@
+using System.Security.Claims;
+using ApplicationLayer.InfrastructureServicesInterfaces;
+using Microsoft.AspNetCore.Http;
+
+namespace Infrastructure.Common
+{
+    public class UserIdProvider(IHttpContextAccessor contextAccessor) : IUserIdProvider
+    {
+        Guid IUserIdProvider.GetUserId()
+        {
+            var claim = contextAccessor.HttpContext!.User.Claims.SingleOrDefault(claim => claim.Type == ClaimTypes.NameIdentifier);
+            if (claim is null)
+            {
+                throw new InvalidOperationException("UserIdProvider call for request with no authorization");
+            }
+            return Guid.Parse(claim.Value);
+        }
+    }
+}