Fix 500 error causing first-time setup wizard to hang

Jellyfin.Api/Auth/CustomAuthenticationHandler.cs

@@ -1,3 +1,4 @@
+using System.Security.Authentication;
 using System.Security.Claims;
 using System.Text.Encodings.Web;
 using System.Threading.Tasks;
@@ -59,6 +60,10 @@ namespace Jellyfin.Api.Auth
 
                 return Task.FromResult(AuthenticateResult.Success(ticket));
             }
+            catch (AuthenticationException ex)
+            {
+                return Task.FromResult(AuthenticateResult.Fail(ex));
+            }
             catch (SecurityException ex)
             {
                 return Task.FromResult(AuthenticateResult.Fail(ex));