Kerberos Interop Issue Between C# NegotiateStream and C++ SSPI (Error 0x80090300)

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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[severity:It's more difficult to complete my work]
Looks like C#'s NegotiateStream and C++ SSPI codes for Kerberos authentication don't understand each other. Does the NegotiateStream use any framing protocol to exchange the Kerberos tokens? If so, kindly provide the same so that it can be adapted in C++ SSPI code.

We have written a POC code with front-end in C# using NegotiateStream and backend in C++ using SSPI with both length preceded token and without length preceded. On the both occasions the backend's AcceptSecurityContext() fails with error 0x80090300.

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Original Comments

Rose Hazel Joy Bigcas (CSI INTERFUSION INC) [MSFT] on 11/11/2025, 01:02 AM:

Thanks for your feedback! To help us better understand this issue, could you please clarify a few points: Is this problem occurring within Visual Studio? If it is related to Visual Studio, could you specify the project type you are using (for example, WinForms, WPF, Console, or other)?

Ravi Korra on 11/20/2025, 00:48 AM:

(private comment, text removed)

Feedback Bot on 11/18/2025, 09:33 PM:

We will close this report in 14 days because we don’t have enough information to investigate further. To keep the problem open, please provide the requested details.

Feedback Bot on 11/26/2025, 07:32 PM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

[jeffhandley]

@wfurt commented: Negotiate stream use custom framing and in general it is meant to only interoperate with itself. If you really want to fiddle with you can get packet capture and possibly inspect the .NET core implementation as it is available publicly.

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