ASP.NET Core 2.0 disable automatic challenge

After some research, I found we can deal with this problem though the bellow approach:

We can add two Authentication scheme both Identity and JWT; and use Identity scheme for authentication and use JWT schema for challenge, JWT will not redirect to any login route while challenge.

services.AddIdentity<ApplicationUser, IdentityRole>().AddEntityFrameworkStores<ApplicationDbContext>();

services.AddAuthentication((cfg =>
{
    cfg.DefaultScheme = IdentityConstants.ApplicationScheme;
    cfg.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
})).AddJwtBearer();

As pointed out by some of the other answers, there is no longer a setting to turn off automatic challenge with cookie authentication. The solution is to override OnRedirectToLogin:

services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
        .AddCookie(options =>
         {                 
             options.Events.OnRedirectToLogin = context =>
             {
                 context.Response.Headers["Location"] = context.RedirectUri;
                 context.Response.StatusCode = 401;
                 return Task.CompletedTask;
             };
         });

This may change in the future: https://github.com/aspnet/Security/issues/1394

Similiar to @Serverin, setting the OnRedirectToLogin of the Application Cookie worked, but must be done in statement following services.AddIdentity in Startup.cs:ConfigureServices:

services.ConfigureApplicationCookie(options => {
  options.Events.OnRedirectToLogin = context => {
    context.Response.Headers["Location"] = context.RedirectUri;
    context.Response.StatusCode = 401;
    return Task.CompletedTask;
  };
});