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Christopher Hertel 0cd5d56164

[Docs] Render the guides with Zensical instead of phpDocumentor (#414 )

* [Docs] Render guides with Zensical, deploy via GitHub Pages actions

phpDocumentor's guide renderer copies the markdown through mostly verbatim:
relative links between pages keep pointing at `*.md` targets that do not exist
in the built site, and nothing validates them, so the published guides are full
of dead links.

Zensical (the Material for MkDocs team's successor to MkDocs) resolves internal
links against the page tree and fails the build on a broken one. `zensical
build --strict` already found four dead links on the first run — three
repo-relative links escaping docs/ (fixed to point at GitHub) and one wrong
in-page anchor.

phpDocumentor stays on for the class-level API reference only; `make docs`
builds the guides into site/ and mounts the reference at site/api/, so its two
header links back to the guides now target the site root.

Deployment moves from pushing a gh-pages branch to the official GitHub Pages
actions, and from release-only to every push on main, with pull requests
building (but not deploying) so a broken link fails review instead of the site.

NOTE: this needs the repository's Pages source switched to "GitHub Actions"
(Settings -> Pages) once.

* [Docs] Adopt the Python SDK's documentation look and feel

The docs site now uses the same theme configuration as
https://py.sdk.modelcontextprotocol.io/ so the language SDKs read as one set
of docs: the MCP mark as logo and favicon, Inter/JetBrains Mono, the
black/slate palette with a three-way (system/light/dark) toggle, instant
navigation, code copy/annotate, and a right-hand table of contents.

The markdown extension set is widened to the same list (tabbed blocks,
task lists, footnotes, emoji/icons, mermaid fences), which the content
restructure builds on.

Styling is otherwise stock: no custom stylesheet, and Zensical's own
`modern` theme variant, pinned explicitly rather than left to the default.

The one departure is code highlighting, which is broken out of the box here:
Pygments only highlights PHP after a `<?php` tag, so the guides — whose code
blocks are almost all fragments — rendered as flat plain text. The `php`
lexer is extended with `startinline`, and complete-file blocks use a
`php-file` lexer that keeps the literal open tag highlighted.

* [Docs] Restructure the guides into task-oriented sections

The guides were ten flat pages, each opening with a hand-maintained table of
contents and each mixing several audiences: `mcp-elements.md` covered tools,
prompts, schema generation and handler-side logging, `transports.md` covered
both transports plus framework integration, and `server-builder.md` covered
configuration, sessions and custom message handlers.

They are now split along the same lines as the Python SDK's documentation
(https://py.sdk.modelcontextprotocol.io/), one topic per page:

  Get started        installation, first server, the Inspector
  Servers            tools, resources, resource templates, prompts,
                     completions, schema generation, registration
  Inside your handler  the ClientGateway, logging
  Running your server  builder, STDIO, HTTP, framework integration,
                     sessions, authorization
  Clients            connecting, transports, capabilities, server-initiated
                     requests, error handling
  Advanced           events, protocol extensions, custom message handlers

Prose is carried over as-is apart from the seams; what is new is the landing
page and one index page per section, which say what the section is for and
where to go next, so no page is a dead end.

The per-page "Table of Contents" lists are gone — the theme renders one from
the headings — and GitHub's `> [!IMPORTANT]` blockquotes became admonitions,
which Zensical renders as callouts rather than plain quotes.

Every code sample and factual claim was then checked against src/ and the
runnable examples, which turned up long-standing errors in the carried-over
prose. Samples that could not run: a prompt using a `system` role (MCP has
only user/assistant), `Mcp\Schema\PromptMessage` (it is under `Schema\Content`)
constructed with an array instead of a single content object,
`Mcp\Capability\Prompt\Completion\ProviderInterface` (it is
`Mcp\Capability\Completion\ProviderInterface`), `new EmbeddedResource(type:,
resource: [...])` (neither parameter exists), a `: resource` return type
(not a PHP type), `#[McpResource]` with a `{path}` variable (that is a
template), a stray quote in the builder example, a `middlewares:` argument
(it is `middleware:`), and `getRequest()->getAttribute()` in the OAuth guide
(no such method — the values arrive on the request meta). Claims corrected:
sampling's `system_prompt` option (it is `systemPrompt`), `SampleMessage`
(it is `SamplingMessage`), `Notification` called an interface (abstract
class), "parameter order matters" for URI templates (bound by name), full
RFC 6570 support (only simple `{var}`), the tool description fallback chain,
`void` returning empty content, a non-zero STDIO exit code, `ErrorEvent`
being null for parse errors, handlers being "prepended", `Psr16StoreSession`,
and PSR-3 log context being sent to the client (it is dropped). Sixteen
`examples/` paths were missing their `server/` segment.

README, the OAuth ADR and one source comment now point at the published site
instead of at markdown files that moved.

* [Docs] Run the docs workflow unfiltered, keep README links relative

The `paths:` filters were mostly noise: `src/**` had to be in the list for
the phpDocumentor build, which meant the workflow ran on nearly every PR
anyway. They also missed two real inputs — `.phpdoc/template/**` and
`composer.lock` — so a template tweak or a phpDocumentor bump could change
the rendered site without triggering a build.

README links go back to relative repo paths. The README is not part of the
Zensical site (`docs_dir` is `docs/`), so those links are only ever resolved
by GitHub and Packagist, where absolute URLs break in-repo navigation for no
gain. The site pointer and the generated API reference stay absolute.

* [Docs] Adopt the doc changes that landed on main into the new structure

Twelve commits landed while the restructure was open, seven of them touching
the flat guides this branch replaces. Renames merged on their own; the three
files that were split apart needed their new sections placed by hand:

- Connection retries, protocol version negotiation, sampling with tools and
  roots from `client.md` into `client/connecting.md` and
  `client/server-requests.md`
- `ResourceLink` and structured output from `mcp-elements.md` into
  `servers/tools.md`
- Protocol version negotiation from `server-builder.md` into
  `run/server-builder.md`

The `setMaxRetries()` note claiming the value is never acted on is gone —
#413 implemented it. Callouts became admonitions and cross-links were
repointed at the new paths, as everywhere else in this branch.

* [Docs] Document the elicitation and roots client examples

Both were missing from the examples guide: the elicitation client predates
this branch, the roots client arrived with #395.

* [Docs] Fold the 2026-07-28 lifecycle into the new structure

Main's stateless-lifecycle.md becomes a docs/lifecycle/ section, and the pages
main touched — deprecations, the middleware split, the client's modern era —
land where the restructure moved them.

* [Docs] Link the Inspector to its documentation, not its repo

* [Docs] Distribute the 2026-07-28 material into the task sections

The Python and TypeScript SDKs file each feature where the task lives and keep
only an era comparison on its own page. Follow them: input-required moves next
to the other handler concerns, caching, subscriptions and era routing to
"Running your server", and one Protocol versions page carries the rest.

* [Docs] Move protocol version negotiation onto the Protocol versions page

The builder page keeps the setProtocolVersion() knob and links out; how a
revision is agreed now sits beside the era it belongs to.

* [Docs] Slim the README to a funnel, turn Examples into an index

* [Docs] Fix the code samples and API listings flagged by the audit

* [Docs] Link the negotiation spec section at latest, not draft

2026-08-20 00:03:54 +02:00

5.6 KiB

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0001 — The MCP server is an OAuth Resource Server, not an Authorization Server

Status: Accepted
Date: 2026-06-15

Context

OAuth 2.1 defines three distinct roles:

Role	What it does	Status in this SDK	Scope
Resource Server	Validates incoming bearer tokens, serves Protected Resource Metadata (RFC 9728), emits `WWW-Authenticate`	Shipped (`AuthorizationMiddleware`, `JwtTokenValidator`, `ProtectedResourceMetadata`)	IN scope
Delegation / proxy to an upstream AS	Forwards `/authorize` and `/token` to your existing IdP	Shipped (`OAuthProxyMiddleware`)	IN scope — delegation ONLY
Authorization Server / Identity Provider (IdP)	Mints its own tokens, registers clients, runs login and consent	Absent	OUT of scope

The SDK repeatedly receives pull requests that move it toward becoming a full OAuth 2.1 authorization server — asking the MCP server to mint its own access and refresh tokens, register clients, and run login and consent flows, that is, to become an Identity Provider. The most explicit example is #373 ("[Server] Add native OAuth 2.1 authorization server", ~3,400 lines across 50+ files), but the direction has crept in incrementally rather than in one PR.

A contributing factor is that the SDK already exposes the authorization-server endpoints in proxy form, and that surface has grown: #221 added the OAuth resource-server middleware, and #269 added Dynamic Client Registration (RFC 7591). Today OAuthProxyMiddleware answers /authorize, /token, and /.well-known/oauth-authorization-server, and DCR endpoints exist. The shape of that surface invites contributors to "finish the job" by backing those endpoints with a real token issuer. It is not scaffolding to be completed — it is a delegating proxy, and that is the whole of its intent.

Decision

The MCP server is an OAuth 2.1 Resource Server that MAY delegate to an upstream authorization server. It will NOT issue tokens or act as an Identity Provider.

Concretely:

The SDK validates bearer tokens, serves RFC 9728 Protected Resource Metadata, and emits WWW-Authenticate challenges. This is the Resource Server role and is fully supported.
The SDK MAY delegate /authorize and /token to an upstream authorization server via OAuthProxyMiddleware. This is delegation only: the middleware redirects the browser to the upstream /authorize endpoint and proxies /token requests to the upstream token endpoint. It never mints, signs, stores, or rotates tokens of its own.
The SDK will NOT implement an authorization server: no token issuance, no token signing or key management, no login UI, no consent UI, no authorization-code or refresh-token storage, no first-party Dynamic Client Registration acting as an issuer.

Pull requests that add authorization-server / IdP behavior are declined by reference to this ADR.

Rationale

Security liability. Issuing tokens means owning signing-key generation, storage, and rotation; authorization-code and refresh-token persistence; refresh-token rotation and replay detection; and consent. A defect in any of these is a credential-issuance vulnerability affecting every consumer of the SDK. This is precisely the surface an MCP SDK should not own.
RFC footprint. A correct authorization server must implement and keep current with RFC 6749 (OAuth 2.0), RFC 7591 (Dynamic Client Registration), RFC 8414 (Authorization Server Metadata), PKCE (RFC 7636), and refresh-token rotation guidance, among others. That is an open-ended maintenance and conformance burden far outside the SDK's purpose.
Mature implementations already exist. Token issuance is a solved problem. league/oauth2-server provides it as a PHP library, and every production IdP — Keycloak, Auth0, Microsoft Entra ID, Okta — provides it as a service. Re-implementing it inside an MCP SDK adds risk without adding value.

Boundary statement

OAuthProxyMiddleware delegates to an upstream IdP. It is not authorization-server scaffolding to be completed. Backing its /authorize and /token endpoints with a first-party token issuer is out of scope and will be declined.

Consequences

The supported authorization architecture is: an external authorization server (your IdP or league/oauth2-server running in your own application) issues tokens; the MCP server validates them as a Resource Server and optionally proxies the OAuth flow to that upstream.
Contributors get a single, citable ruling for why authorization-server PRs are declined, reducing repeated large-PR churn.
Resource Server and proxy/delegation features remain welcome and supported.

Alternatives / what to do instead

If you need an authorization server (token issuance, client registration, login, consent), do not add it to this SDK. Instead:

Front the MCP server with an existing IdP — Keycloak, Auth0, Microsoft Entra ID, or Okta. Point JwtTokenValidator and ProtectedResourceMetadata at that issuer, and optionally use OAuthProxyMiddleware to delegate /authorize and /token to it.
Run league/oauth2-server in your own application, behind the SDK's existing proxy and validator seams. The MCP server validates the tokens it issues; it does not issue them itself.

See ../docs/run/authorization.md for the supported Resource Server and delegation setup.

5.6 KiB Raw Blame History