Passthrough Authentication not working along with oauth

[orathee]

I have set the mcp server (1.18.0) using oauth. User able to login and query the datasources perfectly. I have added an Proxy functionality on Client side so that user can query the datasources using proxy also.

When proxy is selected I am generating the jwt using direct trust connected with below code. Token is generating successfully for the proxy user.

Now when i switch from oauth user to proxy user, I am changing the headers dynamically and passing the credentials token to mcp server but mcp server reject it with 401 error. In file logger logs nothing is logged for this rejection.

@app.get("/api/datasources")
async def get_datasources(req: Request, proxy: str = ""):
    session_id = req.cookies.get("chat_session")
    if not session_id or session_id not in user_sessions:
        raise HTTPException(status_code=401, detail="Unauthorized")

    print(f"\n--- DEBUG: Fetching datasources (Proxy: '{proxy}') ---", flush=True)

    if proxy:
        try:
            print(f"1. Requesting Tableau REST API token for {proxy}...", flush=True)
            proxy_token = await get_proxy_tableau_token(proxy)
            print(f"2. Success! Got Proxy Token: {proxy_token[:15]}...", flush=True)
            
            # 🚀 FIX: Use ONLY the Passthrough token (and the mandatory SSE header)
            mcp_headers = {
                "X-tableau-auth": proxy_token
            }
            
            print(f"   [PROXY DEBUG] Sending headers to MCP: {list(mcp_headers.keys())}", flush=True)
            
        except Exception as e:
            print(f"❌ ERROR in get_proxy_tableau_token: {e}", flush=True)
            raise HTTPException(status_code=403, detail="Proxy authentication failed")
    else:
        # 🚀 FIX: This is the missing block for normal users!
        access_token = user_sessions[session_id]["token"]
        mcp_headers = {
            "Authorization": f"Bearer {access_token}",
            "Accept": "text/event-stream"
        }

    try:
        print(f"3. Connecting to MCP server at {BASE_MCP_URL} with headers: {list(mcp_headers.keys())}", flush=True)
        async with streamablehttp_client(BASE_MCP_URL, headers=mcp_headers) as streams:
            async with ClientSession(streams[0], streams[1]) as client_session:
                await client_session.initialize()
                print("4. MCP Session Initialized. Calling list-datasources...", flush=True)
                
                result = await client_session.call_tool(
                    "list-datasources", 
                    arguments={"limit": 100, "pageSize": 100}
                )

I have tried to change X-tableau-auth to X-Tableau-Auth and included "Accept": "text/event-stream" in header but it still doesn't work. I am on tableau cloud and mcp is setup locally and ENABLE_PASSTHROUGH_AUTH=true in env file. For initial user with oauth everything is working fine but when real user change to proxy view then mcp server reject with 401 error. Please help. Not sure if its related to jwt scopes or something else but i am lost here since 12 hours.

@anyoung-tableau

[anyoung-tableau]

I think I see what's happening. If you don't provide the X-Tableau-Auth header in the Initialize request and only provide the bearer token on the Authorization header, the session "remembers" that and continues to favor the bearer token for subsequent tool calls.

This feels like a bug, but could you please try only providing the X-Tableau-Auth header for all requests, even the Initialize request and see if you can confirm that behavior?

Edit: this may actually not be a bug. The warning on the docs says:

Additionally, if OAuth is enabled, all requests to the MCP server must include the X-Tableau-Auth header, otherwise the client will be considered unauthorized and will be forced to authenticate using OAuth. This even includes MCP lifecycle requests like the Initialization request, even though it does not make any downstream Tableau REST API calls.

[anyoung-tableau]

Oh, interesting. So far I've been testing on a pre-prod Cloud environment and everything is working fine as I'd expect. But when I switched to https://us-east-1.online.tableau.com I am seeing the same behavior as you. This could be an expected change in behavior that is rolling out in newer builds or something. Let me sync up with the team that owns this API on Monday to confirm which scope should be necessary, both currently and going forward.

[orathee]

Thanks

[orathee]

Now i reverted whole code to main branch. The scope "tableau::" is working fine with standalone python script to pass the get query current session. However in app its now failing on next step. Now there is entry of proxy user in mcp server logs.

{"timestamp":"2026-04-05T08:08:12.215Z","message":{"type":"tool","requestId":1,"username":"proxyuser@cisco.com","tool":{"name":"list-datasources","args":{"pageSize":100,"limit":100}}},"level":"debug","logger":"tableau-mcp"}
{"timestamp":"2026-04-05T08:08:12.217Z","message":{"type":"request","requestId":1,"method":"get","url":"https://us-east-1.online.tableau.com/api/3.28/sites/f1efcab9-1202f2077d3c/datasources?filter=&pageSize=100&pageNumber=undefined","headers":{"Accept":"application/json, text/plain, */*","X-Tableau-Auth":"<redacted>","User-Agent":"tableau-mcp/1.18.1 (mcp 0.1.0)"},"params":{"filter":"","pageSize":100}},"level":"info","logger":"rest-api"}
{"timestamp":"2026-04-05T08:08:12.491Z","message":{"type":"response","requestId":1,"url":"https://us-east-1.online.tableau.com/api/3.28/sites/f1efcab9-1202f2077d3c/datasources","status":401,"headers":{"date":"Sun, 05 Apr 2026 08:08:12 GMT","content-type":"application/json","content-length":"120","connection":"keep-alive","global-session-header":"MTAuNzcuNjIuMjQ2OjgwODA=","x-content-type-options":"nosniff","strict-transport-security":"max-age=31536000; includeSubDomains, max-age=31536000; includeSubDomains, max-age=31536000; includeSubDomains, max-age=31536000; includeSubDomains","tableau_error_source":"Client","p3p":"CP=\"NON\"","tableau_error_code":"0x285DFA77","tableau_service_name":"vizportal","x-xss-protection":"1; mode=block","referrer-policy":"strict-origin-when-cross-origin","x-tableau":"Tableau Server","x-edge-shared-cache-skip":"1","x-ua-compatible":"IE=Edge","tableau_status_code":"16","server":"sfdcedge","x-sfdc-request-id":"6ed22a0ad915866a7c9dd5d8102f07df","x-request-id":"6ed22a0ad915866a7c9dd5d8102f07df"},"data":{"error":{"summary":"Unauthorized Access","detail":"Invalid authentication credentials were provided.","code":"401002"}}},"level":"info","logger":"rest-api"}
{"timestamp":"2026-04-05T08:08:12.492Z","message":{"message":"Request failed with status code 401","name":"AxiosError","stack":"AxiosError: Request failed with status code 401\n    at $n (C:\\Users\\tableau-mcp\\build\\index.js:103:1087)\n    at IncomingMessage.<anonymous> (C:\\Users\\tableau-mcp\\build\\index.js:104:12367)\n    at IncomingMessage.emit (node:events:520:35)\n    at endReadableNT (node:internal/streams/readable:1701:12)\n    at process.processTicksAndRejections (node:internal/process/task_queues:89:21)\n    at Ps.request (C:\\Users\\tableau-mcp\\build\\index.js:106:2055)\n    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)\n    at async lG.request (C:\\Users\\tableau-mcp\\build\\index.js:112:4325)\n    at async hl.listDatasources (C:\\Users\\tableau-mcp\\build\\index.js:112:54856)\n    at async getDataFn (C:\\Users\\tableau-mcp\\build\\index.js:245:538)\n    at async $c (C:\\Users\\tableau-mcp\\build\\index.js:196:1099)\n    at async callback (C:\\Users\\tableau-mcp\\build\\index.js:245:403)\n    at async le (C:\\Users\\tableau-mcp\\build\\index.js:127:60462)\n    at async callback (C:\\Users\\tableau-mcp\\build\\index.js:245:298)\n    at async ye.logAndExecute (C:\\Users\\tableau-mcp\\build\\index.js:127:66627)","config":{"transitional":{"silentJSONParsing":true,"forcedJSONParsing":true,"clarifyTimeoutError":false,"legacyInterceptorReqResOrdering":true},"adapter":["xhr","http","fetch"],"transformRequest":[null],"transformResponse":[null],"timeout":600000,"xsrfCookieName":"XSRF-TOKEN","xsrfHeaderName":"X-XSRF-TOKEN","maxContentLength":-1,"maxBodyLength":-1,"env":{},"headers":{"Accept":"application/json, text/plain, */*","X-Tableau-Auth":"m-WwVTZaQXK0a5K5DoZU2g|O|f1efcab9-eeb7-42e1-acf1-1202f2077d3c","User-Agent":"tableau-mcp/1.18.1 (mcp 0.1.0)","Accept-Encoding":"gzip, compress, deflate, br"},"signal":{},"baseURL":"https://us-east-1.online.tableau.com/api/3.28","method":"get","url":"/sites/f1efcab9-1202f2077d3c/datasources","params":{"filter":"","pageSize":100},"allowAbsoluteUrls":true},"code":"ERR_BAD_REQUEST","status":401},"level":"error","logger":"tool"}

Proxy user session is initialized but it is failing when list datasources tool is called. This is what appear in app terminal now.

2. Success! Got Proxy Token: m-WwVTZaQXK0a5K...
   [PROXY DEBUG] Sending headers to MCP: ['X-Tableau-Auth', 'Accept']
3. Connecting to MCP server at http://127.0.0.1:3927/tableau-mcp with headers: ['X-Tableau-Auth', 'Accept']
4. MCP Session Initialized. Calling list-datasources...
5. Success! Got datasources from MCP.
❌ MCP returned non-JSON response: requestId: 1, error: Request failed with status code 401
INFO:     127.0.0.1:65087 - "GET /api/datasources?proxy=proxyuser HTTP/1.1" 200 OK

The only time it is working when i commented out the code in passthrough ts file and used dummy user values. Looks like mcp server tools doesn't work when CA JWT is generated with tableau:: scope

[orathee]

Edit:

Its working fine these scopes in CA JWT "scp": ["tableau::","tableau:viz_data_service:read","tableau:content:read"]

Please inform when there is update on minimum scopes required with CA JWT so that it work with all MCP tools.

[anyoung-tableau]

I spoke with the team that owns the Get Current Server Session API and it looks like it requiring the tableau:*:* scope on the JWT was a bug and is fixed in the upcoming release. Once the fix is live, that scope will no longer be necessary and the only scopes the JWT will need are the ones required by the APIs called by whichever MCP tools you call.

For the full list of scopes and which scopes are used by each individual tool, please refer to https://github.com/tableau/tableau-mcp/blob/main/src/server/oauth/scopes.ts

[orathee]

Thanks. I found another bug in list datasource tool. Will create another thread