Add PublicUrl support for reverse proxy handling

Introduced a `PUBLIC_URL` environment variable to configure the
public URL for OAuth callbacks and reverse proxy scenarios. Updated
`Program.cs` to rewrite request scheme and host based on `PublicUrl`.
Replaced `Microsoft.AspNetCore.Components.Authorization` with
`Microsoft.AspNetCore.Components.Authentication`. Added `PublicUrl`
to `appsettings.json` with a default empty value.

src/BirthList.Web/Program.cs

@@ -1,6 +1,10 @@
+using System.Data;
 using BirthList.Infrastructure.Persistence;
 using BirthList.Web.Authorization;
+using BirthList.Web.Components;
+using BirthList.Web.Components.Account;
 using BirthList.Web.Configuration;
+using BirthList.Web.Data;
 using BirthList.Web.Features.Registries;
 using BirthList.Web.Services;
 using Microsoft.AspNetCore.Components.Authorization;
@@ -9,10 +13,6 @@ using Microsoft.AspNetCore.Identity;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Storage;
-using BirthList.Web.Components;
-using BirthList.Web.Components.Account;
-using BirthList.Web.Data;
-using System.Data;
 
 var builder = WebApplication.CreateBuilder(args);
 
@@ -159,6 +159,20 @@ else
 }
 
 app.UseForwardedHeaders();
+
+var publicUrl = app.Configuration["PublicUrl"];
+if (!string.IsNullOrWhiteSpace(publicUrl) && Uri.TryCreate(publicUrl, UriKind.Absolute, out var publicUri))
+{
+    app.Use(async (context, next) =>
+    {
+        context.Request.Scheme = publicUri.Scheme;
+        context.Request.Host = publicUri.IsDefaultPort
+            ? new Microsoft.AspNetCore.Http.HostString(publicUri.Host)
+            : new Microsoft.AspNetCore.Http.HostString(publicUri.Host, publicUri.Port);
+        await next();
+    });
+}
+
 app.UseHttpsRedirection();
 
 app.UseStaticFiles();