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[BUG] lsproxy 3.0.4.19 mid-request TLS renegotiation on decrypted connections returns empty response bodies to Microsoft OneAuth clients — breaks Microsoft Teams sign-in fleet-wide
Environment: Lightspeed Filter Smart Agent, lsproxy.exe 3.0.4.19 Windows 11, build 10.0.26200.8457 Microsoft Teams 26163.405.4842.717, WebView2 Runtime 150.0.4078.48 Agent configured with machine-wide PAC ( http://relay.lsaccess.me:6544/local.pac ) Symptom: Clicking Sign in in Microsoft Teams opens the sign-in popup, which remains permanently white/blank. Affects all managed devices running the Filter Agent. No block pages are shown and no connections appear blocked (all TCP traffic to the local proxy succeeds), which made this very difficult to diagnose. Root cause identified: Before displaying the sign-in page, Teams' auth library (OneAuth) performs federation provider discovery against https://odc.officeapps.live.com/odc/emailhrd/getfederationprovider?domain=<tenant-domain> . When lsproxy SSL-decrypts this connection, it performs a TLS renegotiation mid-request (after the GET is sent, before the response is delivered). Browser clients and curl tolerate the renegotiation and receive the correct body; OneAuth's client does not, and receives a zero-byte response body. OneAuth then fails with: ServerTemporarilyUnavailable {"ErrorCode":"102","Message":"Federation provider discovery returned an invalid result.","Tag":"76lb9"} (from the MSTeams client log). With discovery failed, Teams never navigates the sign-in WebView2 to any URL, producing the blank window. Reproduction (curl through lsproxy): curl -v --proxy http://127.0.0.1:62312 " https://odc.officeapps.live.com/odc/emailhrd/getfederationprovider?domain=dcboces.org " Output: < Via: mitm/20230626, lsproxy.exe 3.0.4.19 [2025-07-30-1542UTC go1.24.4] windows * schannel: remote party requests renegotiation * schannel: renegotiating SSL/TLS connection confirming the domain is being MITMed and renegotiated. Process Monitor captures of ms-teams.exe show the corresponding WinINET cache entries for federationprovider and hrd written with EndOfFile: 0 (empty bodies) on every attempt. Workaround: Adding officeapps.live.com to both the allow list and the SSL decryption bypass list resolves the issue immediately. Request: Fix lsproxy's TLS handling so decrypted connections do not use mid-stream renegotiation (or otherwise deliver intact response bodies to non-browser TLS clients such as Microsoft OneAuth/WinINET). This affects any OneAuth-based Microsoft sign-in flow (Teams, Office activation, OneDrive) on any decrypted endpoint, so per-domain bypasses are only a partial mitigation. Confirm whether a newer Smart Agent release addresses this. Consider adding Microsoft identity/discovery endpoints (including odc.officeapps.live.com ) to the default decryption bypass set.
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