fix(security): trusted-proxy ForwardedHeaders so LoginThrottle keys on the real client IP (plan R2-07 T2)

src/ZB.MOM.WW.ScadaBridge.Host/Program.cs

@@ -337,6 +337,18 @@ try
         }
 
         // Middleware pipeline
+
+        // Trusted-proxy forwarded headers (arch-review R2 N2): behind Traefik every client
+        // shares the proxy's IP, collapsing the LoginThrottle's {username}|{ip} keys onto
+        // one address (per-IP isolation gone + cheap username-lockout DoS). When enabled,
+        // X-Forwarded-For from the CONFIGURED proxies only is honored. MUST run first —
+        // everything downstream keys on Connection.RemoteIpAddress.
+        var forwardedOptions = builder.Configuration
+            .GetSection(ZB.MOM.WW.ScadaBridge.Security.ForwardedHeadersSecurityOptions.SectionName)
+            .Get<ZB.MOM.WW.ScadaBridge.Security.ForwardedHeadersSecurityOptions>() ?? new();
+        if (ZB.MOM.WW.ScadaBridge.Security.ForwardedHeadersSetup.Build(forwardedOptions) is { } fho)
+            app.UseForwardedHeaders(fho);
+
         app.UseWebSockets();
         app.UseRouting();
         app.UseAuthentication();

src/ZB.MOM.WW.ScadaBridge.Security/ForwardedHeadersSetup.cs

@@ -0,0 +1,64 @@
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.HttpOverrides;
+using System.Net;
+
+namespace ZB.MOM.WW.ScadaBridge.Security;
+
+/// <summary>
+/// Config shape for trusted-proxy forwarded-header handling
+/// (<c>ScadaBridge:Security:ForwardedHeaders</c>). Disabled by default: a deployment
+/// with no reverse proxy must NOT honor X-Forwarded-For (a client could spoof its
+/// throttle key). The documented Traefik topologies enable it with the docker
+/// network range so LoginThrottle keys on the REAL client IP (arch-review R2 N2).
+/// </summary>
+public sealed class ForwardedHeadersSecurityOptions
+{
+    /// <summary>Configuration section binding this options class.</summary>
+    public const string SectionName = "ScadaBridge:Security:ForwardedHeaders";
+
+    /// <summary>Whether X-Forwarded-For from trusted proxies is honored.</summary>
+    public bool Enabled { get; set; }
+
+    /// <summary>Exact proxy IPs allowed to supply X-Forwarded-For.</summary>
+    public string[] KnownProxies { get; set; } = [];
+
+    /// <summary>CIDR networks allowed to supply X-Forwarded-For (e.g. "172.16.0.0/12").</summary>
+    public string[] KnownNetworks { get; set; } = [];
+}
+
+/// <summary>
+/// Builds the <see cref="ForwardedHeadersOptions"/> for <c>app.UseForwardedHeaders</c>.
+/// Pure and fail-fast: malformed entries throw at startup rather than silently
+/// trusting nothing/everything. Defaults (loopback) are CLEARED — only the
+/// explicitly configured proxies/networks are trusted, and ForwardLimit=1 means
+/// only the entry the trusted proxy itself appended is honored.
+/// </summary>
+public static class ForwardedHeadersSetup
+{
+    /// <summary>
+    /// Builds the forwarded-headers options, or <see langword="null"/> when disabled.
+    /// </summary>
+    /// <param name="options">The bound <see cref="ForwardedHeadersSecurityOptions"/>.</param>
+    /// <returns>The configured <see cref="ForwardedHeadersOptions"/>, or <see langword="null"/> when disabled.</returns>
+    public static ForwardedHeadersOptions? Build(ForwardedHeadersSecurityOptions options)
+    {
+        if (!options.Enabled) return null;
+        var built = new ForwardedHeadersOptions
+        {
+            ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto,
+            ForwardLimit = 1,
+        };
+        built.KnownProxies.Clear();
+        // KnownIPNetworks (System.Net.IPNetwork) is the net10 successor to the now-deprecated
+        // KnownNetworks; UseForwardedHeaders reads it identically.
+        built.KnownIPNetworks.Clear();
+        foreach (var proxy in options.KnownProxies)
+            built.KnownProxies.Add(IPAddress.Parse(proxy));
+        foreach (var network in options.KnownNetworks)
+        {
+            var parts = network.Split('/');
+            built.KnownIPNetworks.Add(new(IPAddress.Parse(parts[0]), int.Parse(parts[1])));
+        }
+        return built;
+    }
+}