diff --git a/ZB.MOM.WW.SPHistorianClient/src/ZB.MOM.WW.SPHistorianClient/Grpc/HistorianGrpcReadOrchestrator.cs b/ZB.MOM.WW.SPHistorianClient/src/ZB.MOM.WW.SPHistorianClient/Grpc/HistorianGrpcReadOrchestrator.cs
index 8fe3f72..d040949 100644
--- a/ZB.MOM.WW.SPHistorianClient/src/ZB.MOM.WW.SPHistorianClient/Grpc/HistorianGrpcReadOrchestrator.cs
+++ b/ZB.MOM.WW.SPHistorianClient/src/ZB.MOM.WW.SPHistorianClient/Grpc/HistorianGrpcReadOrchestrator.cs
@@ -5,6 +5,7 @@ using ZB.MOM.WW.SPHistorianClient.Models;
 using ZB.MOM.WW.SPHistorianClient.Wcf;
 using GrpcHistory = ArchestrA.Grpc.Contract.History;
 using GrpcRetrieval = ArchestrA.Grpc.Contract.Retrieval;
+using GrpcStorage = ArchestrA.Grpc.Contract.Storage;
 
 namespace ZB.MOM.WW.SPHistorianClient.Grpc;
 
@@ -16,17 +17,19 @@ namespace ZB.MOM.WW.SPHistorianClient.Grpc;
 ///
 /// Operation mapping (2020 WCF → 2023 R2 gRPC):
 ///   Hist.GetInterfaceVersion → HistoryService.GetInterfaceVersion
-///   Hist.ValidateClientCredential (loop) → HistoryService.ExchangeKey (loop)
+///   Hist.ValidateClientCredential (loop) → StorageService.ValidateClientCredential (loop)
 ///   Hist.OpenConnection2 → HistoryService.OpenConnection
 ///   Retr.StartQuery2 → RetrievalService.StartQuery
 ///   Retr.GetNextQueryResultBuffer2 (loop) → RetrievalService.GetNextQueryResultBuffer (loop)
 ///   Retr.EndQuery2 → RetrievalService.EndQuery
 ///
-/// NOTE: not yet live-verified against a 2023 R2 server. The auth handshake uses
-/// HistoryService.ExchangeKey because the gRPC HistoryService dropped ValidateClientCredential
-/// (it now lives only on StorageService) and gained ExchangeKey with the identical
-/// handle+token→token shape. If a live server rejects this, the handshake op is the first thing
-/// to revisit — everything else is the proven 2020 byte protocol.
+/// AUTH: the SSPI/Negotiate token loop runs through StorageService.ValidateClientCredential
+/// (Handle + InBuff → Status + OutBuff) — per the 2023 R2 contract analysis, that op carries the
+/// NTLM/SSPI tokens (the field names inBuff/outBuff match the 2020 native contract), whereas
+/// HistoryService.ExchangeKey is a separate key-exchange/cert op (NOT the credential handshake).
+/// OpenConnection and the retrieval chain stay on their original services; the server correlates
+/// the validated context by the handshake GUID handle. Live-verified 2026-06-19 against a 2023 R2
+/// server (wonder-sql-vd03) — earlier ExchangeKey wiring was rejected at token round 0.
 /// </summary>
 internal sealed class HistorianGrpcReadOrchestrator
 {
@@ -162,18 +165,19 @@ internal sealed class HistorianGrpcReadOrchestrator
     {
         Guid contextKey = Guid.NewGuid();
         var historyClient = new GrpcHistory.HistoryService.HistoryServiceClient(connection.Channel);
+        var storageClient = new GrpcStorage.StorageService.StorageServiceClient(connection.Channel);
 
         historyClient.GetInterfaceVersion(new GrpcHistory.GetInterfaceVersionRequest(), connection.Metadata, Deadline(), cancellationToken);
 
         HistorianNativeHandshake.RunTokenRounds(
             (handle, wrapped, _) =>
             {
-                GrpcHistory.ExchangeKeyResponse response = historyClient.ExchangeKey(
-                    new GrpcHistory.ExchangeKeyRequest { StrHandle = handle, BtInput = ByteString.CopyFrom(wrapped) },
+                GrpcStorage.ValidateClientCredentialResponse response = storageClient.ValidateClientCredential(
+                    new GrpcStorage.ValidateClientCredentialRequest { Handle = handle, InBuff = ByteString.CopyFrom(wrapped) },
                     connection.Metadata,
                     Deadline(),
                     cancellationToken);
-                byte[] serverOutput = response.BtOutput?.ToByteArray() ?? [];
+                byte[] serverOutput = response.OutBuff?.ToByteArray() ?? [];
                 byte[] error = response.Status?.BtError?.ToByteArray() ?? [];
                 bool success = response.Status?.BSuccess ?? false;
                 return new HistorianNativeHandshake.TokenExchangeResult(success, serverOutput, error);