In my asp net core backend I use Windows Authentication to secure some endpoints. In my Programm.cs I add the Authentication/Authorization like that:

builder.Services.AddAuthentication(NegotiateDefaults.AuthenticationScheme).AddNegotiate();

builder.Services.AddAuthorization(options =>
{
    options.AddPolicy("SoftwarePolicy", policy =>
    {
    policy.RequireRole(@"Mygroup");
    });
});

This works perfectly fine in the browser and it also works when using a private browsing tab (then a window opens and i first have to login to access the endpoint)

Now back to my problem:
I want to grant access to my backend for another developer, so I created a dev tunnel

I configured it like that:
Tunnel Type: Persistent
Access: Public

Now if I want to access the api using the dev tunnel a login window opens,then I login with the same information as I always do, but now it always says Unauthorized or forbidden

The access to endpoints without Authentication works fine.

I tried different Policies e. g. RequireUserName with my username but I still get no access