Initial commit: Add project files

src/KArtSell.Host/Security/DevelopmentHeaderAuthenticationHandler.cs

@@ -0,0 +1,46 @@
+using System.Security.Claims;
+using System.Text.Encodings.Web;
+using Microsoft.AspNetCore.Authentication;
+using Microsoft.Extensions.Options;
+
+namespace KArtSell.Host.Security;
+
+/// <summary>
+/// Development-only authentication. Never enable outside Development.
+/// Required headers: X-KArtSell-User and X-KArtSell-Role.
+/// </summary>
+public sealed class DevelopmentHeaderAuthenticationHandler(
+    IOptionsMonitor<AuthenticationSchemeOptions> options,
+    ILoggerFactory logger,
+    UrlEncoder encoder,
+    IWebHostEnvironment environment)
+    : AuthenticationHandler<AuthenticationSchemeOptions>(options, logger, encoder)
+{
+    protected override Task<AuthenticateResult> HandleAuthenticateAsync()
+    {
+        if (!environment.IsDevelopment())
+        {
+            return Task.FromResult(AuthenticateResult.Fail(
+                "Development header authentication is disabled outside Development."));
+        }
+
+        var user = Request.Headers["X-KArtSell-User"].ToString();
+        var role = Request.Headers["X-KArtSell-Role"].ToString();
+        if (string.IsNullOrWhiteSpace(user) || string.IsNullOrWhiteSpace(role))
+        {
+            return Task.FromResult(AuthenticateResult.NoResult());
+        }
+
+        var claims = new[]
+        {
+            new Claim(ClaimTypes.NameIdentifier, user),
+            new Claim(ClaimTypes.Name, user),
+            new Claim(ClaimTypes.Role, role),
+            new Claim("auth_mode", "development_header")
+        };
+        var identity = new ClaimsIdentity(claims, Scheme.Name);
+        var principal = new ClaimsPrincipal(identity);
+        return Task.FromResult(AuthenticateResult.Success(
+            new AuthenticationTicket(principal, Scheme.Name)));
+    }
+}