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feat(model): preserve tool authentication scheme metadata - #1398

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starsy:feat/tool-security-schemes
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feat(model): preserve tool authentication scheme metadata#1398
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starsy:feat/tool-security-schemes

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@starsy

@starsy starsy commented Oct 27, 2026

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ChatGPT-compatible MCP tools need to advertise top-level securitySchemes. The current typed Tool model cannot emit this field, and deserialization drops it. Applications therefore need a local SDK patch to preserve the declaration.

This change adds optional Tool.security_schemes and a matching builder. It preserves noauth and OAuth scope objects through typed tool catalogs. Existing constructors leave the field unset, so tools without this extension retain their JSON representation. Application _meta remains independent.

The field follows draft SEP-1488. It describes authentication requirements only. It does not validate credentials, change permissions, or alter transport behavior. This implements interoperability support while the proposal remains a draft.

Verification on macOS ARM64 with Rust 1.98.0:

  • 227 library tests and 34 focused integration tests pass, including four new metadata tests.
  • Changed production line coverage is 7/7, or 100% of compiler-mapped executable lines.
  • Stable cargo fmt --all --check passes. The existing nightly-only formatting options produce warnings under stable.
  • Server-only (server,transport-io) and client-only feature checks pass without compiler warnings.
  • cargo clippy -p rmcp --lib --features client -- -D warnings reports 13 result_large_err diagnostics. The same command reports the same 13 locations on unmodified 3.8.0. This PR includes no unrelated lint fixes. The upstream pinned 1.96 toolchain and nightly formatter were not installed for this local check.

The patch is based on rmcp-v3.8.0 (cd88056ffdc97756fbd98e5a12bbeb41758f0ce8).

Design discussion: SEP-1488 already discusses this wire field. This draft proposes the narrow SDK change for review. Please advise if the SDK should expose general descriptor extensions instead while the SEP remains a draft.

An existing downstream integration uses this field for ChatGPT custom MCP connections. OpenAI's authenticated server example also emits it. No downstream application code or credentials are included.

@starsy
[BU-163]feat(model): preserve tool authentication scheme metadata
a3fe58e 
Add the optional securitySchemes field and a matching Tool builder for clients that consume draft SEP-1488 metadata. Omit the field when unset and retain separate application metadata. The declarations describe authentication requirements and do not change credential or permission enforcement.

Verify legacy payload compatibility, noauth and OAuth scope round trips, default constructors, typed tool catalogs, and trait-based tool construction. Focused tests pass. Rust 1.98 Clippy reports the same 13 result_large_err diagnostics on the unmodified 3.8.0 base; no unrelated lint changes are included.
@github-actions github-actions Bot added T-test Testing related changes T-core Core library changes T-handler Handler implementation changes T-model Model/data structure changes labels Oct 27, 2026
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github-actions Bot requested a review from gocamille October 27, 2026 08:57
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github-actions Bot commented Oct 27, 2026

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@gocamille is on triage rotation this week and is the reviewer for this one.

Labels come from the PR labeler. Please review the change.

Automated triage. Labels are a first pass and the assigned maintainer has the final say.

@starsy starsy changed the title [BU-163]feat(model): preserve tool authentication scheme metadata feat(model): preserve tool authentication scheme metadata Oct 27, 2026
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starsy marked this pull request as ready for review October 27, 2026 18:34
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starsy requested a review from a team as a code owner October 27, 2026 18:34
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@gocamille

gocamille commented Oct 30, 2026

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Thanks for this, @starsy! On your question at the end, I'd rather not add either a typed field or a general extension while SEP-1488 is a draft, since the thread there has been moving toward advisory scopeHints and _meta is the spec's place for extensions today. OpenAI's reference lists _meta["securitySchemes"] as a mirror for clients that only read _meta. Have you tried whether ChatGPT picks it up from _meta alone? If it does, this already works on main; if it doesn't, @DaleSeo I think it's worth deciding whether we carry a draft field for it.

@starsy

starsy commented Nov 2, 2026

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Thanks for pointing this out @gocamille. We have now tested _meta["securitySchemes"] alone. A fresh ChatGPT custom MCP connection completed OAuth, discovered the tools, and successfully called an authenticated tool without the top-level field. Our earlier claim that ChatGPT requires it was too strong.

Given this result, I propose closing this PR. We’ll update our downstream integration to use _meta["securitySchemes"] with upstream rmcp and validate that dependency change separately. There is no demonstrated need to add the typed field for our tested ChatGPT flow. We can revisit it after the protocol settles on a standard representation.

@starsy starsy closed this Nov 2, 2026
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