Just two notes from when I was adding these helpful code bits to my project that may help others:
If you’re just going to connect from the wasm to the host, extend BaseAddressAuthorizationMessageHandler instead of AuthorizationMessageHandler. It sets the URL for you so you don’t need the ConfigureHandler() call.
You need to put your MessageHandler into the services, e.g.
builder.Services.AddScoped<Auth0MessageHandler>(); builder.Services.AddHttpClient("ServerAPI", client => client.BaseAddress = new Uri(builder.HostEnvironment.BaseAddress)) .AddHttpMessageHandler<Auth0MessageHandler>();