Best possible solution:

Close this helper-only duplicate and continue review on #97781, preserving the route-level bounded-read, SDK cloud-token-host, and overflow coverage there.

Do we have a high-confidence way to reproduce the issue?

Yes, by source inspection. Current main and v2026.6.11 still use raw response.json() in the helper, while the live registered sign-in routes still delegate through SDK handlers.

Is this the best way to solve the issue?

No for this branch as the landing path. The bounded-reader direction is useful, but the canonical route-level PR is the narrower maintainable endpoint because it covers the live registered routes and sovereign-cloud token host behavior.

Security review:

Security review cleared: No supply-chain or secret-handling regression was found; the diff narrows an external SSO response-read boundary and adds only a focused test.

AGENTS.md: found and applied where relevant.

What I checked:

• Repository policy read: Root AGENTS.md and scoped extensions/AGENTS.md were read fully; extension boundary and ClawSweeper duplicate/supersession guidance shaped the review. (AGENTS.md:1, 3d206140f3f0)
• Current main helper behavior: Current main still parses successful Bot Framework User Token responses with raw response.json() in callUserTokenService, which is the helper-level read this PR changes. (extensions/msteams/src/sso.ts:133, 3d206140f3f0)
• Current main live route behavior: Current main registers signin.token-exchange and signin.verify-state through SDK delegates, so a helper-only change does not cover the wider production route boundary. (extensions/msteams/src/monitor.ts:516, 3d206140f3f0)
• Latest release still has the same gap: v2026.6.11 still contains the raw helper response.json() read and SDK-delegated sign-in route registrations, so the SSO hardening is not shipped yet. (extensions/msteams/src/sso.ts:133, e085fa1a3ffd)
• Current PR scope: Live PR metadata shows this branch changes only extensions/msteams/src/sso.ts and extensions/msteams/src/monitor-handler.sso.test.ts; it does not touch monitor.ts route registration. (extensions/msteams/src/sso.ts:134, 96b784c37c80)
• Canonical PR state: The open canonical PR is non-draft, mergeable, proof-positive, and changes monitor.ts, sso.ts, sdk.ts, and route-level tests for the same SSO bounded-read problem. (extensions/msteams/src/monitor.ts:554, efffccc03c29)

Likely related people:

• sudie-codes: Authored the merged Microsoft Teams SSO implementation that added callUserTokenService, the invoke handlers, and adjacent SSO tests. (role: introduced behavior; confidence: high; commits: 828ebd43d47b; files: extensions/msteams/src/sso.ts, extensions/msteams/src/monitor.ts, extensions/msteams/src/monitor-handler.sso.test.ts)
• heyitsaamir: Authored the merged Teams SDK migration that established the current SDK sign-in delegate boundary for the live routes. (role: major refactor author; confidence: high; commits: 04c29825356f; files: extensions/msteams/src/monitor.ts, extensions/msteams/src/sdk.ts, extensions/msteams/src/sso.ts)
• steipete: Merged the Teams SDK migration that owns the production route compatibility question now handled by the canonical PR. (role: merger; confidence: high; commits: 04c29825356f; files: extensions/msteams/src/monitor.ts, extensions/msteams/src/sdk.ts)
• Alix-007: Authored the shared bounded provider JSON reader and owns the open canonical Microsoft Teams SSO route-level bounded-read PR. (role: canonical fix author and adjacent owner; confidence: high; commits: 2592f8a51a4e, efffccc03c29; files: src/agents/provider-http-errors.ts, src/agents/provider-http-errors.test.ts, extensions/msteams/src/sso.ts)
• Vincent Koc: Recent carry-forward work touched the Microsoft Teams SSO and monitor files on current main. (role: recent area contributor; confidence: medium; commits: 3ad77774f0e5; files: extensions/msteams/src/sso.ts, extensions/msteams/src/monitor.ts)

Codex review notes: model internal, reasoning high; reviewed against 3d206140f3f0.