Windows SSPI to Java GSSAPI interoperability to achieve SSO on EJB calls

Question

I have Java client running on Windows machine that calls remote EJB on JBoss EAP/Wildfly running on Linux machine. I use Kerberos to achieve SSO. Java client verifies the user against Windows domain and pass his identity within EJB call to the JBoss server.

I started with JAAS and the builtin com.sun.security.auth.module.Krb5LoginModule. It works correctly except one thing: user has to type his username and password again. So, it is not a real SSO.

The problem is that Windows prohibits to export kerberos session key from its LSA credential cache. It can be fixed by setting a specific Windows registry key on each client machine - but this is not acceptable for the customer.

Therefore I am trying to find an alternative solution. I learned that Windows provides SSPI that shall be interoperable with GSSAPI used by Java. I use Waffle library to access SSPI from Java on the client. On the server I keep using JAAS, because it runs on Linux so I cannot use Waffle there.

I also learned that I don't need to implement LoginModule, rather I need SASL client.

So, I had a look how com.sun.security.sasl.gsskerb.GssKrb5Client works and I am trying to reimplement it using Waffle.

First step seems to work correctly - I obtain SSPI security context from Waffle, then get the initial token and send it to the server. The server accepts the token and respond with its own token.

And now the problem comes. In the original SASL client the 'unwrap' operation is used to extract data from the server token, and 'wrap' operation is used to create reply token to be sent to server.

GSSAPI wrap / unwrap operations shall correspond to SSPI EncryptMessage / DecryptMessage operations according to Microsoft doc. This two methods are not available in Waflle, but are available in NetAccountClient library.

However, I am not able to use them correctly. If I use a single SECBUFFER_STREAM then the DecryptMessage is succesfull, however the data part of the token is not extracted and I don't know how to determine the offset where it begins.

If I use SECBUFFER_STREAM and SECBUFFER_DATA as suggested by Microsoft docs, then I get an error: com.sun.jna.platform.win32.Win32Exception: The message or signature supplied for verification has been altered

I also tried other combinations of SECBUFFER types as suggested elsewhere, but without success.

Any idea what am I doing wrong ?

To source code of unwrap method:

    public byte[] unwrap(byte[] wrapper) throws LoginException {
        Sspi.SecBuffer.ByReference inBuffer = new Sspi.SecBuffer.ByReference(Secur32Ext.SECBUFFER_STREAM, wrapper);
        Sspi.SecBuffer.ByReference buffer = new Sspi.SecBuffer.ByReference();
        buffer.BufferType = Sspi.SECBUFFER_DATA;
        Secur32Ext.SecBufferDesc2 buffers = new Secur32Ext.SecBufferDesc2(inBuffer, buffer);

        NativeLongByReference pfQOP = new NativeLongByReference();

        int responseCode = Secur32Ext.INSTANCE.DecryptMessage(secCtx.getHandle(), buffers, new NativeLong(1), pfQOP);


        if (responseCode != W32Errors.SEC_E_OK) {
            throw handleError(responseCode);
        }

        byte[] data = buffer.getBytes();
        return data;
    }