diff --git a/src/Controllers/ExternalLoginController.cs b/src/Controllers/ExternalLoginController.cs
index 86e1435..b97747f 100644
--- a/src/Controllers/ExternalLoginController.cs
+++ b/src/Controllers/ExternalLoginController.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Security.Claims;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Authorization;
@@ -63,6 +64,16 @@ namespace SteamOpenIdConnectProvider.Controllers
             var userName = info.Principal.FindFirstValue(ClaimTypes.Name);
             var userId = info.Principal.FindFirstValue(ClaimTypes.NameIdentifier);
 
+            if (string.IsNullOrEmpty(userId))
+            {
+                throw new ArgumentNullException(nameof(userId), $"No claim found for {ClaimTypes.NameIdentifier}");
+            }
+
+            if (string.IsNullOrEmpty(userName))
+            {
+                userName = userId.Split('/').Last();
+            }
+
             var user = new IdentityUser { UserName = userName, Id = userId };
 
             _userManager.UserValidators.Clear();