# Inspector V2 — Authorization hardening (MCP 2026-07-28)

### [Brief](README.md) | [V2 Scope](v2_scope.md) | [Mid-session auth](v2_auth_mid_session.md) | [EMA / XAA](v2_auth_ema.md) | [Smoke testing](v2_auth_smoke_testing.md)

Align Inspector v2 with the **authorization hardening** in the upcoming MCP **`2026-07-28`** specification release — six SEPs that tighten OAuth/OIDC client behavior for MCP's single-client, many-server deployment pattern.

## Summary

The [2026-07-28 release candidate](https://blog.modelcontextprotocol.io/posts/2026-07-28-release-candidate/) adds six authorization SEPs. All are **OAuth client** requirements. Inspector implements OAuth through a mix of SDK delegation (connect-time standard OAuth via `auth()`) and local code (EMA wire, storage, web callback, mid-session recovery).

**Strategy:** Upgrade to the v2 TypeScript SDK (`@modelcontextprotocol/client`) when its auth-hardening PRs land. Do **not** reimplement SDK OAuth logic in Inspector — delegate connect-time standard OAuth to the SDK and wire the gaps (callback parameters, storage shape, client type). **Mid-session authorization** is a separate, near-term track ([Mid-session auth](v2_auth_mid_session.md)); this doc covers connect-time and storage hardening that mid-session builds on.

## Normative references

- [MCP authorization (draft — 2026-07-28 RC target)](https://modelcontextprotocol.io/specification/draft/basic/authorization)
- [MCP authorization (2025-11-25 — current stable)](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization)
- [2026-07-28 RC announcement — Authorization Hardening](https://blog.modelcontextprotocol.io/posts/2026-07-28-release-candidate/#authorization-hardening)
- [RFC 9207](https://www.rfc-editor.org/rfc/rfc9207) — OAuth 2.0 Authorization Server Issuer Identification (`iss` parameter)
- [RFC 6750 §3.1](https://datatracker.ietf.org/doc/html/rfc6750#section-3.1) — Bearer token `insufficient_scope`
- TypeScript SDK tracking: [modelcontextprotocol/typescript-sdk](https://github.com/modelcontextprotocol/typescript-sdk) issues `#2197`–`#2201`, `#2198`, `#2256`; PRs `#2265`, `#2271`, `#2272`

## Relationship to mid-session auth

[Mid-session auth](v2_auth_mid_session.md) ships in the **near term**. Overlap:

| Concern | Mid-session spec | This doc |
| ------- | ---------------- | -------- |
| **SEP-2350** scope union on 403 step-up | `handleAuthChallenge()` owns union + UX for runtime challenges | Connect-time step-up inherits SDK union after v2 upgrade; mid-session still uses `saveScope(authorizationScopes)` in the challenge handler |
| **SEP-2207** refresh / `offline_access` | EMA legs 2–3 re-mint; standard OAuth silent refresh | Connect-time scope selection and DCR metadata |
| **SEP-2468** `iss` validation | Applies to any interactive re-auth redirect (401 mid-session) | Connect-time callback wiring is the first place to land `iss` passthrough |
| **SEP-2352** issuer-bound credentials | Re-register after AS migration may surface as mid-session failure | Storage and `invalidateCredentials` must be correct before mid-session recovery can succeed |

Implement mid-session auth now. Land auth hardening on the v2 SDK upgrade path without blocking mid-session work — use compatible storage and callback shapes so both tracks merge cleanly.

## The six SEPs

| SEP | Requirement | Primary owner |
| --- | ------------- | ------------- |
| **[SEP-2468](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2468)** | Validate `iss` on authorization responses per RFC 9207; reject mix-up across authorization servers | Client (+ SDK reference impl) |
| **[SEP-837](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/837)** | Declare OIDC `application_type` during Dynamic Client Registration (`native` vs `web`) | Client (+ SDK DCR body) |
| **[SEP-2352](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2352)** | Bind persisted DCR credentials to the AS `issuer`; re-register when resource migrates between ASes | Client storage (+ SDK AS-change detection) |
| **[SEP-2207](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2207)** | Request refresh tokens from OIDC-style ASes (`offline_access` in scope when appropriate); do not assume refresh tokens are issued | Client (+ SDK `determineScope`) |
| **[SEP-2350](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2350)** | On 403 step-up, re-authorize with **union** of previously requested scopes and challenge scopes; on 401 re-login, **replace** scope | Client (+ SDK transport retry for direct transport) |
| **[SEP-2351](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2351)** | Stable RFC 8414 `.well-known` discovery suffix for authorization and resource metadata | Spec / discovery (SDK helpers) |

Servers emit per-operation scopes in 403 challenges (SEP-2350 server posture). Inspector consumes them; server-side scope-challenge middleware is out of scope unless needed for tests.

## SDK vs Inspector responsibilities

Inspector today uses **`@modelcontextprotocol/sdk` ^1.29.0** (v1 monolith). Auth hardening lands on **v2 `main`** (`@modelcontextprotocol/client`). Upgrade is part of this work.

```text
Connect-time standard OAuth          EMA                         Web remote backend
───────────────────────────          ───                         ──────────────────
SDK auth() + BaseOAuthClientProvider  Local wire (ema/)           Frozen token stub
OAuthStorage keyed by serverUrl       IdP OIDC in idpOidc.ts      No interactive OAuth
completeOAuthFlow(code) only          No SDK CrossAppAccess       Mid-session → browser
```

### What the v2 SDK provides (after upgrade)

| SEP | SDK status (Jun 2026) | Inspector gets |
| --- | --------------------- | -------------- |
| SEP-2207 | Implemented on v2 `main` ([#2199](https://github.com/modelcontextprotocol/typescript-sdk/issues/2199)) | `offline_access` augmentation in authorize scope for standard OAuth via `auth()` |
| SEP-2350 | Open PR [#2265](https://github.com/modelcontextprotocol/typescript-sdk/pull/2265) | `unionScopes()` + 403 retry uses union on streamable HTTP direct transport |
| SEP-2352 | Open PR [#2271](https://github.com/modelcontextprotocol/typescript-sdk/pull/2271) | AS migration detection → `invalidateCredentials` → re-DCR |
| SEP-2468 | Open PR [#2272](https://github.com/modelcontextprotocol/typescript-sdk/pull/2272) | `iss` validation in code-exchange path when host passes `iss` |
| SEP-837 | Open [#2198](https://github.com/modelcontextprotocol/typescript-sdk/issues/2198) | `application_type` in DCR request body |
| SEP-2351 | Tracking [#2256](https://github.com/modelcontextprotocol/typescript-sdk/issues/2256) | Discovery URL suffix in SDK metadata helpers |

### What Inspector must still implement

| SEP | Inspector work | Why not SDK-only |
| --- | -------------- | ---------------- |
| SEP-2468 | Parse `iss` from OAuth callback URL; extend `completeOAuthFlow(code, iss?)`; pass through to SDK `auth()` | Host owns the redirect handler — SDK cannot read the callback URL |
| SEP-837 | Ensure web vs TUI/CLI set correct client type (`web` / `native`) in provider metadata or environment | SDK may infer from redirect URI; Inspector must not mis-declare cross-environment |
| SEP-2352 | Key `OAuthStorage` credentials by AS `issuer` (not only `serverUrl`); implement `invalidateCredentials` on `BaseOAuthClientProvider`; migrate shared `oauth.json` | Storage is Inspector-owned; SDK calls provider hooks |
| SEP-2207 | EMA leg 1 already requests `openid offline_access` (`IDP_OIDC_SCOPES`); verify standard OAuth path after upgrade | EMA bypasses SDK authorize for leg 1 |
| SEP-2350 | Mid-session union in `handleAuthChallenge()` + `saveScope(authorizationScopes)`; web/EMA paths bypass SDK transport retry | See [Mid-session auth](v2_auth_mid_session.md) |
| SEP-2351 | Verify discovery after upgrade; no duplicate discovery logic in Inspector | Uses SDK `discoverOAuthProtectedResourceMetadata` today |

**Do not duplicate** SDK `auth.ts` logic (RFC 9207 decision table, AS migration edge cases, scope union helpers). Upgrade and wire.

## Implementation strategy

### Principles

1. **Delegate** connect-time standard OAuth to the v2 SDK `auth()` flow.
2. **Wire** callback parameters, storage, and client-type metadata in Inspector.
3. **Extend** EMA and mid-session paths locally where the SDK has no EMA/XAA API.
4. **Upgrade** from `@modelcontextprotocol/sdk` v1 to v2 packages as a gated step — not a silent dependency bump.

### Order of work

| Step | When | Work |
| ---- | ---- | ---- |
| 1 | **Now (parallel with mid-session auth)** | Compatible prep: callback type includes optional `iss`; storage schema reserves `authorizationServerIssuer`; mid-session `saveScope(union)` per [Mid-session auth](v2_auth_mid_session.md) |
| 2 | **When v2 SDK auth PRs merge** | Upgrade to `@modelcontextprotocol/client`; run existing OAuth integration tests |
| 3 | **Immediately after upgrade** | SEP-2468 callback passthrough; SEP-2352 storage + `invalidateCredentials`; SEP-837 client type per environment |
| 4 | **Verify** | Smoke scenarios in [v2_auth_smoke_testing.md](v2_auth_smoke_testing.md); add hardening-specific cases |

Land order in the SDK (maintainer plan): **SEP-2350 → SEP-2352 → SEP-2468**, with **SEP-837** in the same auth-release series.

### Per-SEP Inspector mapping

#### SEP-2468 — `iss` validation (RFC 9207)

- **Web:** `App.tsx` OAuth callback — read `iss` from query string alongside `code`; pass to `InspectorClient.completeOAuthFlow(code, iss?)`.
- **TUI / CLI:** Node callback server — same passthrough.
- **Core:** `OAuthManager.completeOAuthFlow` forwards `iss` to SDK `auth()`.
- **EMA:** Leg 1 OIDC callback is separate (`completeEmaIdpAuthorizationAndMint`); evaluate whether IdP responses require `iss` validation on the OIDC path (may reuse SDK OIDC helpers after upgrade).

#### SEP-837 — `application_type` in DCR

- **Web (`BrowserOAuthClientProvider`):** `application_type: "web"` (https redirect).
- **TUI / CLI:** `application_type: "native"` (localhost / custom scheme redirect).
- **Pre-registered clients:** N/A — no DCR.
- **CIMD:** Portable client IDs — no `application_type` on DCR.

#### SEP-2352 — credentials bound to AS issuer

- Extend `ServerOAuthState` / `oauth.json` with `authorizationServerIssuer` (or key storage by issuer + resource).
- Implement `OAuthClientProvider.invalidateCredentials(scope)` on `BaseOAuthClientProvider` — clear client info and/or tokens per SDK request.
- On AS migration (PRM `authorization_servers` change), SDK triggers invalidation; Inspector storage must honor it and allow re-DCR.
- **CIMD carve-out:** HTTPS `client_id` URLs remain portable across AS changes; tokens still invalidate per SDK behavior.

#### SEP-2207 — OIDC refresh token guidance

- **Standard OAuth:** Inherited from v2 SDK `determineScope()` after upgrade.
- **EMA leg 1:** Already requests `openid offline_access`; IdP refresh in `refreshIdpOidcSession`.
- **Mid-session:** Silent refresh and EMA re-mint per [Mid-session auth](v2_auth_mid_session.md); do not assume refresh tokens exist.

#### SEP-2350 — step-up scope accumulation

- **Connect-time (direct transport):** v2 SDK transport 403 retry after [#2265](https://github.com/modelcontextprotocol/typescript-sdk/pull/2265).
- **Mid-session:** `handleAuthChallenge()` computes `authorizationScopes = union(previous, required)`; `saveScope` after success. Standard OAuth step-up = interactive; EMA step-up = silent legs 2–3 when IdP session valid.
- **401 re-login:** Replace scope set (not union) — mid-session and connect-time.

#### SEP-2351 — discovery suffix

- Rely on v2 SDK discovery helpers used by `auth()`, CIMD (`core/auth/cimd.ts`), and EMA (`core/auth/ema/resourceContext.ts`).
- No Inspector-specific discovery URL construction unless regression found in smoke tests.

## Non-goals

- Reimplementing MCP authorization-server or resource-server wire formats.
- v1 / v1.5 backport.
- **Client credentials grant** ([#1225](https://github.com/modelcontextprotocol/inspector/issues/1225)) — separate track.
- Full MCP **2026-07-28 stateless transport** migration (separate from auth hardening).
- Server-side scope-challenge middleware in Inspector test servers beyond what [Mid-session auth](v2_auth_mid_session.md) requires for 403 fixtures.

## Testing

| SEP | Test |
| --- | ---- |
| SEP-2468 | Callback with matching `iss` succeeds; mismatched `iss` rejected; AS advertising support without `iss` rejected |
| SEP-837 | DCR succeeds for web (https redirect) and TUI/CLI (localhost redirect) against OIDC AS requiring `application_type` |
| SEP-2352 | Simulated AS migration in PRM → credentials invalidated → re-DCR → connect succeeds |
| SEP-2207 | Authorize request includes `offline_access` when AS advertises it; connect succeeds without refresh token when AS omits one |
| SEP-2350 | Connect-time and mid-session 403 step-up use union scopes; 401 re-login replaces scopes |
| SEP-2351 | Discovery resolves against draft suffix paths |

Document manual scenarios in [v2_auth_smoke_testing.md](v2_auth_smoke_testing.md) after implementation.

## File touch list (expected)

| Area | Files |
| ---- | ----- |
| Upgrade | Root and client `package.json`; import paths v1 → v2 |
| Callback | `clients/web/src/App.tsx`, `core/auth/node/oauth-callback-server.ts`, `core/mcp/oauthManager.ts`, `core/mcp/inspectorClient.ts` |
| Provider | `core/auth/providers.ts`, `core/auth/browser/providers.ts` |
| Storage | `core/auth/store.ts`, `core/auth/oauth-storage.ts`, `core/mcp/remote/node/remoteOAuthStorage.ts` (if landed) |
| Mid-session overlap | `core/auth/challenge.ts`, `core/mcp/oauthManager.ts` (`handleAuthChallenge`, `saveScope`) — see [Mid-session auth](v2_auth_mid_session.md) |
| Tests | `clients/web/src/test/core/auth/`, `clients/web/src/test/integration/mcp/inspectorClient-oauth*.test.ts` |
| Smoke doc | `specification/v2_auth_smoke_testing.md` |

## Related specs

| Doc | Relationship |
| --- | ------------ |
| [v2_auth_mid_session.md](v2_auth_mid_session.md) | Mid-session auth (near term); owns runtime SEP-2350 behavior and most recovery UX |
| [v2_auth_ema.md](v2_auth_ema.md) | EMA legs 1–3; SEP-2207 leg 1 scopes; future v2 SDK Layer-2 helpers |
| [v2_auth_smoke_testing.md](v2_auth_smoke_testing.md) | Manual verification ladder |
| [v2_scope.md](v2_scope.md) | OAuth handling scope item |
| [v2_storage.md](v2_storage.md) | Shared `oauth.json` — issuer-keyed credentials affect storage schema |