Security hardening: MCP server auth#540
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Pull request overview
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Adds security hardening for MCP integrations by introducing opt-in MCP server authentication and default URL validation to mitigate client-side SSRF risks.
Changes:
- Add
requireAuthhook toMcpPluginto gate inbound MCP/mcprequests with 401 on failure. - Add
validateMcpServerUrlURL gate (scheme + DNS/private-network filtering) and exposeallowPrivateNetwork/validateUrlparams in the MCP client. - Add/adjust Jest tests to cover URL validation and server auth behavior.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.
Show a summary per file
| File | Description |
|---|---|
| external/mcpclient/src/url-validation.ts | Implements default URL scheme + private-network/DNS-based validation and error type. |
| external/mcpclient/src/url-validation.spec.ts | Adds unit tests for URL validation behavior and edge cases. |
| external/mcpclient/src/mcp-client-types.ts | Extends client params with allowPrivateNetwork and validateUrl. |
| external/mcpclient/src/mcp-client-plugin.ts | Wires URL validation into MCP client creation flow. |
| external/mcpclient/src/mcp-client-plugin.spec.ts | Stubs DNS lookup to keep existing tests deterministic/offline. |
| external/mcp/src/plugin.ts | Adds requireAuth option, startup warning, and auth middleware for MCP SSE route prefix. |
| external/mcp/src/plugin.spec.ts | Adds unit tests for new checkAuth behavior with various outcomes. |
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corinagum
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Per team decision, the MCP client SSRF guard adds friction for legitimate on-prem MCP customers and the underlying risk is low-likelihood. Reverting the client-side URL validation work; the McpPlugin server auth (#14) and the Express-level path-prefix middleware refactor are kept. Removes: - external/mcpclient/src/url-validation.ts (and spec) - McpClientPluginParams.allowPrivateNetwork + validateUrl - validateMcpServerUrl call in makeMcpClient - DNS mock added to mcp-client-plugin.spec.ts
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In checkAuth, after the requireAuth try/catch, return early without writing a 401 if req.aborted is set. The client has already disconnected; attempting to set headers on a destroyed stream produces noisy warnings without changing observable behavior. Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
lilyydu
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May 27, 2026
## Summary Adds a Trust Model page under Essentials → App Configuration documenting the layered authentication model the SDK uses for inbound JSON Web Tokens. ## Why A scanner flagged the SDK's `JsonWebToken` accessor class because it does not perform signature verification at the point of token parsing. A cross-SDK audit confirmed this is intentional architecture: signature verification runs at the HTTP boundary (via the activity pipeline's token validator), and the accessor class is a typed view over already-validated payloads. Every consumer of decoded claims is downstream of a validator pass. This page makes the architectural invariant explicit for SDK consumers, reviewers, and future contributors. ## What's covered - What the SDK validates automatically on `/api/messages` (signature, issuer, audience, lifetime, algorithm) - What downstream code can rely on (typed accessors over validated tokens) - How to add custom authentication to non-default surfaces (MCP, callbacks, webhooks) — references the `requireAuth` hook recently added in microsoft/teams.ts#540 / microsoft/teams.net#448 - Anti-patterns to avoid (constructing the accessor from untrusted input as a basis for authorization decisions) ## Build verified `npm run build` clean. ## Related PRs - TypeScript: microsoft/teams.ts#586 - Python: microsoft/teams.py#432 - .NET: microsoft/teams.net#517 --------- Co-authored-by: Copilot Autofix powered by AI <[email protected]>
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Summary
Addresses security scan finding #14 (MCP server mounted without auth). TypeScript half of a 2-SDK PR set (.NET PR is on the same branch name).
#14 — MCP server auth
New opt-in
requireAuthhook onMcpPluginOptions:Hook is called once per inbound MCP request via an Express-level prefix middleware on
/mcp(covers any current or future handler registered under that path).false/throw returns 401. When unset, all requests are accepted and a one-time startup warning fires when the SSE transport comes up.Design doc
design/mcp-server-auth-options.mdE2E verified
/mcpreturns 401 without auth, SSE handshake on correct bearer/api/messages): bot responded to a devtools chat message withREQUIRE_AUTH=1active simultaneouslyrequireAuthis unset; silent when set