Windows Authentication for .NET Core 2.2 not working - 401 unauthorized

Question

I have an ASP.NET Core webserver that is running on .NET Core 2.2 and was previously able to handle Windows Authentication. This feature wasn't tested for a long time though, and now I'm trying to reactivate it. The frondend is running Angular, and there seems to be no special settings involved on the fronend side. Still, I always get a 401 unauthorized error when calling the windowslogin endpoint. Here's the controller code that was previously there and hasn't been modified:

  [Authorize(AuthenticationSchemes = "Windows")]        
    [HttpPost]
    [Route("windowslogin")]
    public IActionResult RequestTokenForWindowsLogin()
    {
        IIdentity windowsIdentity;
        try
        {
            windowsIdentity = Request.HttpContext.User.Identity;
        }
        catch (Exception ex)
        {
          ...
        }

        IUserInfo user = UserService.GetIccUserFromWindowsUser(windowsIdentity);
        if (user == null) {
            return Forbid();
        }
        IActionResult token = CreateToken(user);
        return token;
    }

The authentication scheme "Windows" wasn't explicitly added in the startup file, so I'm not sure which changed I have to make. I already checked the Windows authentication checkbox in the project settings and activated it in the Windows IIS settings on my local machine.

This is most of the startup.cs:

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        
    
         services.AddAuthentication(IISDefaults.AuthenticationScheme)          
           .AddJwtBearer("Default", options =>
        {
            options.Events = new JwtBearerEvents{   OnMessageReceived = handleAuthTokenInQuery};
            options.TokenValidationParameters = new TokenValidationParameters
            {
                ValidateIssuer = true,
                ValidateAudience = true,
                ValidateLifetime = true,
                ValidateIssuerSigningKey = true,
                ValidIssuer = Configuration["SecurityKeyIssuer"],
                ValidAudience = Configuration["SecurityKeyAudience"],
                IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["SecurityKey"]))
            };
        })
        .AddJwtBearer("AzureAD", options =>
         {
          ...
         });

        services.AddAuthorization(options =>
        {
            options.DefaultPolicy = new AuthorizationPolicyBuilder()
           .RequireAuthenticatedUser()
           .AddAuthenticationSchemes("Default", "AzureAD")
           .Build();
        });

        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        services.AddMemoryCache();    
        services.AddCors(o => o.AddPolicy("AllowAnyOrigin", builder =>
        {
            builder.WithOrigins("http://locahost:4000")
                   //.AllowAnyOrigin()
                   .AllowAnyMethod()
                   .AllowAnyHeader()
                   .SetIsOriginAllowed((x) => true)
                   .AllowCredentials();
        }));

        services.AddSignalR();

        services.AddSpaStaticFiles(configuration =>
        {
            configuration.RootPath = "ClientApp/dist";
        });
   
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, IHubContext<AppHub> signalRHub, IAppService appService, IZeitbuchungService zeitbuchungService, IChatService chatService)
    {

        AppHub.GlobalContext = signalRHub;

        List<string> origins = Configuration.GetSection("Origins:value").Get<List<string>>();        
        app.UseCors("AllowAnyOrigin");
        app.UseHsts();
     
        app.UseAuthentication();           

        app.UseStaticFiles();
        app.UseSpaStaticFiles();            

        app.UseSignalR(routes =>
        {
            routes.MapHub<AppHub>("/apphub");
        });

        app.UseMvc(routes => { routes.MapRoute(name: "default", template: "{controller}/{action=Index}/{id?}"); });
        app.UseSpa(spa => { spa.Options.SourcePath = "ClientApp"; });
        SqlDependency.Start(Configuration["Database:ConnectionString"]);


    }