ASP.net-core 3.0 - Is it possible to return custom error page when user is not in a policy? - asp.net-core

Question

I'm creating an intranet website and I'm having some trouble with the authentication part. I would like to limit the access for a controller to users in a specific Active Directory Roles. If the user is not in the specified Roles, then it should redirect him to a custom error page.
Windows authentication is enabled. I've tried the following solutions :
I created a custom policy in my ConfigureServices method inside my Startup.cs :
...
services.AddAuthorization(options =>
{
options.AddPolicy("ADRoleOnly", policy =>
{
policy.RequireAuthenticatedUser();
policy.RequireRole(Configuration["SecuritySettings:ADGroup"], Configuration["SecuritySettings:AdminGroup"]);
});
});
services.AddAuthentication(IISDefaults.AuthenticationScheme);
....
with inside my appsettings.json my active directory groups (not the one i'm really using of course) :
"SecuritySettings": {
"ADGroup": "MyDomain\\MyADGroup",
"AdminGroup": "MyDomain\\MyAdminGroup"
}}
and inside my Configure method :
...
app.UseAuthorization();
app.UseAuthentication();
app.UseStatusCodePagesWithReExecute("/Home/ErrorCode/{0}");
...
I have the following controller :
[Area("CRUD")]
[Authorize(Policy = "ADRoleOnly")]
public class MyController : Controller
I have a HomeController with the following method :
[AllowAnonymous]
public IActionResult ErrorCode(string id)
{
return View();
}
but when I debug my site, this method is never reached.
If I'm a user inside one of the specified roles of my policy, it's all working as expected.
But if I'm not a member of the roles, I'm redirected to the default navigator page.
I would like to redirect to a custom error page. I thought that was the purpose of
app.UseStatusCodePagesWithReExecute("/Home/ErrorCode/{0}");

Answer 1

It will generate a 403 statuscode when the policy fails,app.UseStatusCodePagesWithReExecute does not detect 403:
UseStatusCodePagesWithReExecute is not working for forbidden (403)
You could write a custom middleware to deal with it :
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
app.UseHsts();
}
app.Use(async (context, next) =>
{
await next();
if (context.Response.StatusCode == 403)
{
var newPath = new PathString("/Home/ErrorCode/403");
var originalPath = context.Request.Path;
var originalQueryString = context.Request.QueryString;
context.Features.Set<IStatusCodeReExecuteFeature>(new StatusCodeReExecuteFeature()
{
OriginalPathBase = context.Request.PathBase.Value,
OriginalPath = originalPath.Value,
OriginalQueryString = originalQueryString.HasValue ? originalQueryString.Value : null,
});
// An endpoint may have already been set. Since we're going to re-invoke the middleware pipeline we need to reset
// the endpoint and route values to ensure things are re-calculated.
context.SetEndpoint(endpoint: null);
var routeValuesFeature = context.Features.Get<IRouteValuesFeature>();
routeValuesFeature?.RouteValues?.Clear();
context.Request.Path = newPath;
try
{
await next();
}
finally
{
context.Request.QueryString = originalQueryString;
context.Request.Path = originalPath;
context.Features.Set<IStatusCodeReExecuteFeature>(null);
}
// which policy failed? need to inform consumer which requirement was not met
//await next();
}
});
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
}