Suppress redirect on API URLs in ASP.NET Core

Question

I have an ASP.NET Core site that uses cookie authentication for most pages. For those pages, the default server response of providing a 302 redirect for an unauthorized client is desirable. However, the site also accepts API requests; they use API keys and have no use for cookies.

Ideally, I'd like to turn off cookie processing for the API URLs altogether, but minimally, I need to ensure that if an API client is unauthorized, the server doesn't respond with a 302 redirect.

Answer 1

Replace the redirect event handler with one that uses the default behavior only if the path is not an API. In Startup.ConfigureServices, add this:

services.ConfigureApplicationCookie(options => {
    options.Events.OnRedirectToAccessDenied = ReplaceRedirector(HttpStatusCode.Forbidden, options.Events.OnRedirectToAccessDenied);
    options.Events.OnRedirectToLogin = ReplaceRedirector(HttpStatusCode.Unauthorized, options.Events.OnRedirectToLogin);
});

Use this helper method to replace the redirect methods:

static Func<RedirectContext<CookieAuthenticationOptions>, Task> ReplaceRedirector(HttpStatusCode statusCode, Func<RedirectContext<CookieAuthenticationOptions>, Task> existingRedirector) =>
    context => {
        if (context.Request.Path.StartsWithSegments("/api")) {
            context.Response.StatusCode = (int)statusCode;
            return Task.CompletedTask;
        }
        return existingRedirector(context);
    };

With this in place, the API controller methods can call Unauthorized() and Forbid() without causing redirects.

Update: The above is for ASP.NET Core 2. The code for ASP.NET Core 1 is different.