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The hosted ish MCP server signs clients in over OAuth and forwards the resulting token to the ish backend. You never paste a token into a config file. For the steps to add the server and sign in, see Connecting; this page documents the auth machinery behind it.

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How sign-in works

The server validates every inbound request and acts as an OAuth resource server. Validation. Inbound Supabase access tokens are verified as ES256 against the project’s JWKS, with audience authenticated. The backend re-validates the same token, so a request is checked twice (defense in depth). Discovery. The server advertises Supabase as its authorization server using two discovery documents: OAuth 2.0 Protected Resource metadata (RFC 9728) at /.well-known/oauth-protected-resource, and Authorization Server metadata (RFC 8414) at /.well-known/oauth-authorization-server. Supabase serves its OAuth metadata at /.well-known/openid-configuration rather than the RFC 8414 path, so the server forwards the OIDC document at the RFC 8414 path and injects a registration_endpoint (Supabase’s Dynamic Client Registration endpoint, which the OIDC document omits). That metadata is what lets a client (Claude Code, Cursor, and others) bootstrap sign-in with no pre-issued token: it discovers Supabase, registers itself over Dynamic Client Registration, runs the OAuth code flow, and presents the resulting access token to the server.

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OAuthProxy

The server fronts Supabase with a FastMCP OAuthProxy instead of pointing clients straight at Supabase. Why it exists. Supabase’s OAuth server validates redirect_uri by exact string match and does not implement the RFC 8252 loopback exception (where an auth server ignores the port for http://127.0.0.1 and http://localhost redirects). A client that binds a fresh ephemeral loopback port per session, with VS Code being the notable one, reuses a cached registered client_id whose redirect_uris no longer match the port it bound, so Supabase rejects the authorize request with invalid redirect_uri. Cursor, Claude Code, and the app builders keep a consistent redirect through register, authorize, and callback, so they never hit this.
The proxy is why VS Code and other ephemeral-loopback-port clients sign in at all. Without it, a cached client_id whose registered ports no longer match would fail at the authorize step. You do not configure any of this; the client picks its port and the proxy absorbs it.
What the proxy does. It advertises this server as the authorization server, presents a full Dynamic Client Registration interface that accepts any loopback port, and holds one fixed redirect registered with Supabase. It translates between the client’s dynamic loopback URI and the fixed upstream one, so every client works regardless of how it picks its redirect. The proxy runs its own PKCE leg upstream (S256). It does not forward RFC 8707 resource indicators, since Supabase does not implement them.

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Token forwarding

Tools never read headers or the local config directly. Each tool obtains the Authorization header to send to api.ishlabs.io through a single chokepoint. The forwarded token is the validated access token, which is the upstream Supabase JWT. The inbound bearer is a short reference token the proxy mints to the client; the proxy resolves it server-side to the stored upstream Supabase JWT, and that JWT is what gets forwarded. If the resolved access-token context is unavailable, the server forwards the inbound Authorization header verbatim; a request with no bearer is rejected. The backend re-validates whatever token it receives, so forwarding is defense in depth rather than the only check.

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Confirm the session

Read the ish://identity/me resource, or call a read-only tool like workspace_get, to see whose account the session is acting as. A read draws no credits. See Connecting for the full check.

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See also

Connecting

Add the server to your client and sign in, step by step.

Tool conventions

Naming, id prefixes, polymorphism, and safety annotations.

MCP resources

Session and reference data, including ish://identity/me.