src/AVEVA.Historian.Client/HistorianClientOptions.cs

@@ -53,6 +53,17 @@ public sealed class HistorianClientOptions
     /// </summary>
     public string? ServerDnsIdentity { get; init; }
 
+    /// <summary>
+    /// Optional WCF "Via" address (e.g. <c>net.tcp://host:42568</c>). When set, the SDK's WCF
+    /// channel factories <b>connect</b> to this address while still addressing the SOAP message
+    /// <c>To</c> the logical endpoint built from <see cref="Host"/>/<see cref="Port"/>. Use this when
+    /// the Historian is reached through a port-forwarding tunnel or proxy whose local port differs
+    /// from the server's real service port: point <see cref="Host"/>/<see cref="Port"/> at the
+    /// server's real endpoint (so the server's WCF AddressFilter matches) and set this to the tunnel
+    /// endpoint. Has no effect on the gRPC transport. Default null (connect == address).
+    /// </summary>
+    public string? ConnectViaAddress { get; init; }
+
     /// <summary>
     /// For <see cref="HistorianTransport.RemoteGrpc"/>: when true the channel uses TLS
     /// (<c>https://</c>); when false it uses plaintext (<c>http://</c>). Matches the stock

src/AVEVA.Historian.Client/Wcf/HistorianWcfClientCredentialsHelper.cs

@@ -2,6 +2,7 @@ using System.IdentityModel.Selectors;
 using System.IdentityModel.Tokens;
 using System.Security.Cryptography.X509Certificates;
 using System.ServiceModel;
+using System.ServiceModel.Description;
 using System.ServiceModel.Security;
 
 namespace AVEVA.Historian.Client.Wcf;
@@ -28,6 +29,14 @@ internal static class HistorianWcfClientCredentialsHelper
                 RevocationMode = X509RevocationMode.NoCheck,
             };
         }
+
+        // Tunnel/proxy support: connect to the Via address while still addressing the message To the
+        // logical endpoint (Host/Port). Lets a port-forward whose local port differs from the server's
+        // real service port satisfy the server-side WCF AddressFilter (which checks the To header).
+        if (!string.IsNullOrWhiteSpace(options.ConnectViaAddress))
+        {
+            factory.Endpoint.EndpointBehaviors.Add(new ClientViaBehavior(new Uri(options.ConnectViaAddress)));
+        }
     }
 
     private sealed class AcceptAnyCertificateValidator : X509CertificateValidator

tests/AVEVA.Historian.Client.Tests/WcfEventReadSpikeTests.cs

@@ -49,6 +49,7 @@ public sealed class WcfEventReadSpikeTests
         string? password = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_PASSWORD");
         string? spn = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_SPN");
         string? dnsId = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_DNSID");
+        string? via = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_VIA");
         bool certificate = string.Equals(
             Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_TRANSPORT"), "certificate", StringComparison.OrdinalIgnoreCase);
         bool allowUntrusted = string.Equals(
@@ -69,6 +70,7 @@ public sealed class WcfEventReadSpikeTests
             TargetSpn = string.IsNullOrWhiteSpace(spn) ? "NT SERVICE\\aahClientAccessPoint" : spn,
             ServerDnsIdentity = string.IsNullOrWhiteSpace(dnsId) ? null : dnsId,
             AllowUntrustedServerCertificate = allowUntrusted,
+            ConnectViaAddress = string.IsNullOrWhiteSpace(via) ? null : via,
         };
 
         HistorianWcfEventOrchestrator orchestrator = new(options);