Windows Authentication using Blazor with .Net Core WebApi - asp.net-core

Question

I have the task to develop a Blazor Webassembly App. This app is only used within the companys network and for security reasons we would like to use the existing AD and NTLM Authentication.
So far I have a minimal Blazor App configured and running in IIS. Its configured to use Windows Authentication and that works so far. When I open the app in Browser I get asked for my credentials.
The app should also communicate with a .net core webapi which is also secured by windows authentication. This webapi security too works as it should. When I open an URL to it in Browser I get asked for my credentials and the page loads as it should.
Now the Problem: When I call the same url (that works in Browser) from my Blazor app with HttpClient.GetAsync I get an "401: Not Authorized" error. Even though the app itself is loaded with the same authentication. Is there something I have to do?
The MSDN Documenations a gigantic and I couldnt find a Solution.
In the WebApi Startup.cs in ConfigureServices() I added
services.AddAuthentication(IISDefaults.AuthenticationScheme);
services.AddAuthorization();
and in Configure()
app.UseCors(x => x.AllowAnyMethod().AllowAnyHeader().SetIsOriginAllowed(origin => true).AllowCredentials());
app.UseAuthentication();
app.UseAuthorization();
PS:
The Blazor App uses .NET Core 3.1
The WebApi uese .NET 5.0

Answer 1

I recommend checking Blazor WebAssembly additional security scenarios (all the examples are there)
To authorize your request, you can use HttpClient with BaseAddressAuthorizationMessageHandler:
builder.Services.AddHttpClient("ServerAPI",
client => client.BaseAddress = new Uri("https://www.example.com/base"))
.AddHttpMessageHandler<BaseAddressAuthorizationMessageHandler>();
BaseAddressAuthorizationMessageHandler will automatically add Authorize header to all outgoing requests.
Note: This works only with Blazor Wasm, not Server.