Disabling Cookie Login Redirects for Known API Endpoints in ASP.NET Core (Pre-.NET 10)

Disabling Cookie Login Redirects for Known API Endpoints in ASP.NET Core (Pre-.NET 10)

In current versions of ASP.NET Core (.NET 6 / 7 / 8), when using Cookie Authentication to protect APIs, unauthenticated or unauthorized requests are not always handled in a way that fits API scenarios. This behavior changes officially starting with .NET 10.

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Previous Behavior (before .NET 10)

• By default, the Cookie Authentication Handler:
  • Redirected unauthenticated/unauthorized requests to the login or access-denied paths.
  • Exception: XHR (Ajax) requests returned 401/403 instead of being redirected.

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New Behavior (from .NET 10 onwards)

• Unauthenticated or unauthorized requests made to known API endpoints now return:
  • 401 Unauthorized
  • 403 Forbidden
    instead of redirecting to login or access-denied pages.
• XHR/Ajax requests always result in 401/403, regardless of the endpoint.

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Why This Matters

• APIs expect proper HTTP status codes (401/403).
• Redirecting to HTML pages can break:
  • SPA clients (React, Angular, Blazor).
  • Mobile applications, which expect JSON or clear status codes.

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Pre-.NET 10 Solution: Customizing Events

Before this new behavior becomes the default in .NET 10, you can customize Cookie Authentication Events to return the correct status codes for API requests.
This solution relies on endpoint metadata to detect API controllers.

Example Code

builder.Services.AddIdentityCookies(o =>
{
    o.ApplicationCookie.Configure(options =>
    {
        options.Cookie.Name = "CookieName";
        options.LoginPath = "/Account/Login";
        options.AccessDeniedPath = "/Account/AccessDenied";
        ...


        options.Events.OnRedirectToLogin = context =>
        {
            if (IsApiControllerEndpoint(context))
            {
                context.Response.StatusCode = StatusCodes.Status401Unauthorized;
            }
            else
            {
                context.Response.Redirect(context.RedirectUri);
            }
            return Task.CompletedTask;
        };

        options.Events.OnRedirectToAccessDenied = context =>
        {
            if (IsApiControllerEndpoint(context))
            {
                context.Response.StatusCode = StatusCodes.Status403Forbidden;
            }
            else
            {
                context.Response.Redirect(context.RedirectUri);
            }
            return Task.CompletedTask;
        };
    });
});

private static bool IsApiControllerEndpoint(RedirectContext<CookieAuthenticationOptions> context)
{
    var endpoint = context.HttpContext.GetEndpoint();
    if (endpoint == null)
        return false;

    // Detect API endpoints via [ApiController] attribute
    return endpoint.Metadata.GetMetadata<ApiControllerAttribute>() != null;
}

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How It Works

• Requests to API controllers ([ApiController]) → return 401 or 403.
• Requests to regular MVC or Razor pages → continue redirecting to login/access-denied pages.
• Cookie security features (HttpOnly, Secure, SameSite, Sliding Expiration) remain active.

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Additional Notes

• [ApiController] detection works for MVC and Web API controllers.

• Minimal APIs and SignalR hubs may need extra handling using:

  • IApiEndpointMetadata
  • or TypedResults

• Testing is essential to confirm:

  • API endpoints return 401/403.
  • MVC/Razor pages still redirect.
  • SPA or mobile clients handle the responses properly.

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Conclusion

• Previous behavior (before .NET 10): all requests were redirected to login/access-denied, except XHR which returned 401/403.
• New behavior (in .NET 10): known API endpoints return 401/403 instead of redirects.
• Workaround (in .NET 6–8): customize cookie authentication events with endpoint metadata to get the new behavior early.