It works: client service + server service + utility service to know server uri when app is running

Components/Pages/Account/Register.razor

@@ -1,6 +1,7 @@
 @page "/register"
 @using Sandbox.Models.ViewModels
 
+@inject Sandbox.App.Services.AuthService.IAuthService AuthService
 @* @inject AuthenticationStateProvider AuthenticationStateProvider *@
 @* @inject NavigationManager NavigationManager *@
 
@@ -51,7 +52,7 @@
 @code {
     [SupplyParameterFromForm] private UserRegister user { get; set; }
 
-    HttpClient _http = new() { BaseAddress = new("https://localhost:7122") };
+    //HttpClient _http = new() { BaseAddress = new("https://localhost:7122") };
 
     private string message = string.Empty;
     private string messageCssClass = string.Empty;
@@ -61,8 +62,9 @@
 
     async Task HandleRegistration()
     {
-        var response = await _http.PostAsJsonAsync("/api/register", user);
-        var result = await response.Content.ReadFromJsonAsync<ServiceResponse<int>>();
+        // var response = await _http.PostAsJsonAsync("/api/register", user);
+        // var result = await response.Content.ReadFromJsonAsync<ServiceResponse<int>>();
+        var result = await AuthService.Register(user);
         message = result.Message;
         messageCssClass = result.Success ? "text-success" : "text-danger";
     }