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Authentication and authorization

Authentication covers the browser product, WebSocket, local MCP, repository tools, and Copilot. A verified GitHub user supplies presence and attribution. Optional instance admission lists restrict who may use Chopin. Browser routes, WebSockets, and the hosted agent intersect the user's repository role with the GitHub App installation. Local MCP instead checks the repository role granted directly to its caller-supplied bearer token.

GitHub App

Create one GitHub App for each deployment. Use these registration settings:

Homepage URL: <APP_ORIGIN>
Callback URL: <APP_ORIGIN>/auth/github/callback
Setup URL:    <APP_ORIGIN>/auth/github/setup
  • Leave Expire user authorization tokens enabled.
  • Leave Request user authorization (OAuth) during installation disabled.
  • Leave device flow disabled for a hosted deployment; local device-flow sign-in (below) requires enabling it on the App instead.
  • Enable Redirect on update when a setup URL is configured.
  • Disable webhooks.
  • Select Any account so personal accounts and organizations can install it.
  • Prefer Only select repositories while installing it.

Repository permissions for the complete product are:

Contents:        Read-only
Pull requests:   Read-only
Checks:          Read-only
Commit statuses: Read-only
Metadata:        Read-only (automatic)

Contents backs file, tree, code-search, and commit-history tools. The other read-only permissions back the hosted GitHub MCP pull-request toolset. Chopin does not request repository, organization, or account write permission. An AGENT=off deployment only needs Contents and automatic Metadata access unless organization admission is enabled.

Organization admission additionally requires:

Organization permissions:
Members: Read-only

The App must be installed on every allowed organization, and an organization owner must approve this permission. Existing installations continue with their old permissions until the owner approves the update.

No App ID, private key, JWT, installation access token, or webhook secret is used. Chopin acts on behalf of each signed-in user with a GitHub App user access token so repository-role checks and the user's Copilot entitlement remain theirs.

Configure Chopin with the App's slug and OAuth client credentials. A minimal production environment contains:

STORAGE_DRIVER=postgres
DATABASE_URL=postgresql://<user>:<password>@<database-host>:5432/<database>
APP_ORIGIN=https://chopin.example
GITHUB_APP_SLUG=chopin-example
GITHUB_APP_CLIENT_ID=...
GITHUB_APP_CLIENT_SECRET=...
GITHUB_ALLOWED_USERS=octocat,hubot
GITHUB_ALLOWED_ORGANIZATIONS=githubnext
SESSION_ENCRYPTION_KEY=<64 hex characters>

The client ID is distinct from the numeric App ID. Generate the encryption key with openssl rand -hex 32; it protects the short-lived OAuth attempt cookie, including state, the PKCE verifier, and an optional browser return path.

APP_ORIGIN must be exactly one HTTP(S) origin: no credentials, path, query, fragment, or trailing slash. HTTPS is required except for loopback development, such as http://127.0.0.1:8787. Callback URLs are built only from this value, never from incoming Host or forwarded headers.

The complete variable reference and deployment procedures live in Self-hosting.

Local device-flow sign-in

AUTH_MODE=local replaces the browser authorization-code flow with GitHub's device flow and persists the resulting credential so a restarted process can resume the same login. It is a loopback-only mode, not an alternative hosted deployment: SERVER_HOST must be 127.0.0.1, ::1, or localhost, and APP_ORIGIN must be an exact HTTP(S) loopback origin on the same port. The Docker image binds 0.0.0.0 and is incompatible with local mode; run from a source checkout instead.

Device flow authenticates with the App's public client ID only. GITHUB_APP_CLIENT_SECRET is not read in local mode; a value left over from a hosted .env is ignored. Enable device flow on the App used for local mode (this is the opposite of the hosted guidance above), and keep Expire user authorization tokens enabled so expiring access and refresh tokens are issued.

The browser flow is:

  1. POST /auth/device requests a device code from GitHub and returns the user-facing code, verification URL, and expiry to the browser. The private device_code never leaves the server. The response also sets an HttpOnly, origin-checked attempt cookie that binds later requests to the same browser.
  2. The browser shows the code and polls GET /auth/device roughly every one to two seconds. The server polls GitHub independently, honoring GitHub's advertised interval and any slow_down increase, so approval from another device or browser still completes the attempt.
  3. Once GitHub reports the grant, the browser calls POST /auth/device/complete, which validates the authorized identity and admission, then attempts credential persistence.
  4. If persistence needs plaintext consent, complete (or the next GET) reports {status: "consent", path}, the exact local file path. The browser shows the plaintext-storage warning; POST /auth/device/consent {accept} either finishes sign-in or cancels it. Declining or dismissing this prompt discards the pending credential and cancels the attempt without creating a session; it does not fall back to an in-memory-only login.
  5. POST /auth/device/cancel cancels an attempt at any point and discards any pending credential.

Device routes do not return 401, which the browser client treats as an invalid session and reloads. A missing attempt cookie reports cancelled; state-changing requests with a mismatched Origin return 403.

Credential persistence prefers the operating system's credential store (macOS Keychain, Windows Credential Manager, or a Linux secret service such as gnome-keyring, through Bun.secrets). That attempt is bounded to five seconds so an unavailable or locked store cannot hang sign-in; a store call that is still in flight when the bound expires is left running and its eventual result is discarded (a late success is deleted, not kept) so it can never resurrect a declined or superseded attempt.

Automated tests exercise this boundary through an injected NativeSecrets implementation (a file-backed fake in Playwright, an in-memory fake in unit tests), not a live OS vault. apps/server/src/auth/local-store.test.ts also has one opt-in test, gated on TEST_NATIVE_SECRETS=1, that round-trips a dummy credential through the real store. That check has only run against Linux libsecret/gnome-keyring; macOS Keychain and Windows Credential Manager behavior is implemented against the same Bun.secrets API but is not yet verified on those platforms. Windows also defaults to CRED_PERSIST_ENTERPRISE (roaming) persistence for Bun.secrets.set; a machine-local persist: "local" option exists in Bun's API but Chopin does not currently set it or verify its behavior.

When the store is missing, inaccessible, disabled, or times out, Chopin keeps the credential in memory and asks for plaintext consent instead of writing anything, using this exact warning and choice text:

System vault not available

The recommended secure storage (keychain, keyring, or credential manager) could not be found or accessed. You may need to install or configure one.

Storing the token in the config file saves it as plain text, which is insecure. If you decline, sign-in will be cancelled and no account state will be changed.

Store token in plain text config file?

Yes, store in plain text (insecure)
No, cancel sign-in

Accepting writes the credential to a JSON file under the directory named by CHOPIN_LOCAL_CREDENTIALS_DIR (default $XDG_CONFIG_HOME/chopin, or ~/.config/chopin on Linux, ~/Library/Application Support/Chopin on macOS, %APPDATA%\Chopin on Windows), with a newly created directory at 0700 and the credential file at 0600 on Unix, and an atomic write-then-rename so a crash mid-write cannot leave a partially written file. These permissions restrict which local account can read the file; they do not encrypt it or make it equivalent to an OS credential store. Chopin never writes it inside the repository or process working directory. Consent applies to this login only: it is not a standing "prefer plaintext" preference for future accounts, and a later secure-store failure during refresh never falls back to writing plaintext silently.

Restoring after a restart uses a separate long-lived, HttpOnly, browser-binding cookie set only on successful sign-in. On the next /api/session call, Chopin loads the persisted credential for that binding, checks the installation, origin, App client ID, and account against the stored record, revalidates or refreshes the token, rechecks identity and admission exactly as a fresh sign-in would, and issues a new ordinary session. Startup still clears every process-local session and Planner ownership, so a restored login does not reclaim Planner ownership or replay interrupted model work; the returning browser only skips repeating the device-flow prompt.

Logout in local mode deletes the persisted credential from whichever backend stored it and clears the session and binding cookies. Because device-issued refresh tokens do not require the client secret, but revoking the grant on GitHub's side does, local logout cannot revoke the GitHub authorization itself; the user must remove it from Settings > Applications on GitHub to fully revoke access. A stale or delayed store write after logout cannot revive the login, because logout also invalidates the browser binding it depended on.

Each browser has its own binding; configured instance admission lists still apply to every authorized account. Loopback binding does not make this a mode for internet-facing or exposed multi-user deployments.

Instance admission

GITHUB_ALLOWED_USERS and GITHUB_ALLOWED_ORGANIZATIONS are optional, comma-separated, case-insensitive GitHub login lists. If both are empty or unset, every verified GitHub user is admitted. If either has entries, a user is admitted when their current username is listed or they have active membership in any listed organization. Explicit usernames therefore also provide a break-glass path when organization verification is unavailable.

Organization checks use the caller's token with GET /user/memberships/orgs/{org}, which sees private membership when the App has Members read access. Pending invitations and outside collaborators are not admitted, nor are billing managers who are not organization members. Public-membership lookup is not used. Organization admission does not restrict repository ownership. Browser and hosted authorization retain separate App installation and repository role checks; local MCP checks the supplied token's repository role directly.

Admission results are cached by a hash of the access token for 30 seconds. Browser requests, open-socket authorization, MCP requests, and Planner permission callbacks recheck the policy. A definitive removal revokes the process-local browser session and Planner ownership at the next browser or socket recheck; a Planner permission callback refuses the operation immediately. GitHub outages, rate limits, malformed responses, blocked Apps, and missing permission fail closed for new requests but do not revoke an established browser session; they are reported as a temporary 503 and retried later.

Configuration is read at process startup. Restart after changing either list; startup already clears every process-local login session. GitHub usernames and organization names can be renamed, so update the lists when that happens.

Authorization and installation

Authorization and installation are separate GitHub App operations. A user may authorize the App without installing it. After sign-in, Chopin lists only the personal and organization installations that user can access and only the repositories selected for each installation. The repository picker links to the App installation page when access has not been installed or needs updating.

The picker loads every repository page in the background and keeps a validated snapshot for the lifetime of the browser tab. Stale snapshots are revalidated page by page with GitHub ETags when search begins. The snapshot is scoped to the GitHub user and cleared on logout, account changes, and the installation setup callback. Listing responses remain no-store; the server forwards conditional requests but does not retain picker repository data.

Local MCP is an intentional exception to this installation boundary. Its bearer token is authenticated independently and authorized with a direct repository lookup. An MCP-created document for a repository outside the App installation is not available through browser routes, WebSockets, or the hosted agent until the installation includes that repository. See Local agent MCP.

The authorization-code flow uses state, S256 PKCE, the exact configured callback, and the App client secret. It does not request OAuth scopes; permissions come from the App registration and each installation. The setup callback ignores GitHub's untrusted installation_id query parameter, clears the browser's installation snapshot, and redirects into the product. The next picker or authorization request re-queries GitHub with the signed-in user's token.

When a signed-out browser opens a document deep link, the sign-in request sends the current path, query, and fragment as return_to. Chopin accepts only one validated root-relative product path, stores it inside the encrypted OAuth attempt cookie, and redirects there after a successful callback. Absolute and protocol-relative URLs, control characters, backslashes, and API, auth, WebSocket, or MCP paths fall back to /; a callback query cannot override the stored value. GitHub App installation setup remains separate: its callback still ignores return paths and redirects to /?repository_access=changed.

Organization members may need an owner to approve installation or new permissions. For an organization using SAML SSO, establish an active SAML session before authorizing. If organization repositories remain absent, revoke the App under Authorized GitHub Apps and authorize it again while that SAML session is active.

Webhooks are intentionally disabled for self-hosted deployments. Installation, repository-selection, and revocation changes are observed through request-time checks with a cache no longer than the one-minute open-socket recheck interval.

Environment-specific callback and proxy configuration is documented in Remote development.

Session boundary

The browser receives an HttpOnly, SameSite=Lax cookie containing a random session ID and a 256-bit secret. The serving process keeps the secret hash, GitHub access and refresh tokens, expirations, user, and credential revision in memory. PostgreSQL receives only the session ID, user ID, expiry, and creation time so durable Planner ownership can reference an active process session. A database row or session ID cannot authenticate a request without the in-memory secret hash.

GitHub App user access tokens expire after eight hours. Chopin refreshes five minutes early, rotates the one-use refresh token, and atomically replaces the process-local credential object. Concurrent requests share one refresh. Logout removes the memory entry before any asynchronous cleanup, so a racing refresh cannot resurrect a session.

A rejected refresh token or a second API 401 deletes the matching local session. Network failures, rate limits, malformed responses, and GitHub 5xx responses do not delete it. A transient proactive refresh may continue using the still-valid access token; after access expiry it reports a temporary error and retains the session for retry.

Sessions expire absolutely after 30 days or whenever the server process stops. In local mode, the session created after a restart is a new session bound to the restored device-flow credential, not the same session ID; see Local device-flow sign-in for the restore path. After acquiring the database writer lease, every new process clears session registry rows and Planner ownership before accepting traffic. Documents, transcripts, reserved Planner context fields, and repository installations remain durable. Logout deletes the process-local session and registry row but does not revoke the GitHub App authorization.

OAuth state, the PKCE verifier, and the validated browser return path are held in a separate encrypted, ten-minute HttpOnly cookie. Browser state-changing routes and WebSocket upgrades require an Origin header exactly equal to APP_ORIGIN. The bearer-authenticated MCP route accepts a missing Origin, as non-browser clients normally omit it, but rejects a present mismatched Origin. Open sockets periodically recheck the process-local session, instance admission, and installation repository permission. On restart, a returning local browser restores a new session on /api/session; hosted browsers return to sign-in.

When a credential rotates, any Planner SDK session holding the previous token is aborted and discarded before refresh. A later turn recreates it from the durable transcript and document. An interrupted turn is not replayed automatically because it may already have made durable tool changes.

Browser HTTP API

GET  /auth/github
GET  /auth/github/callback
GET  /auth/github/install
GET  /auth/github/setup
GET  /api/session
GET  /api/github/installations?page=1
GET  /api/github/installations/:installationId/repositories?page=1
GET  /api/repositories/:owner/:repository/channels
POST /api/repositories/:owner/:repository/channels
GET  /api/repositories/:owner/:repository/documents/:slug
GET  /api/channels/:channelId
PATCH /api/channels/:channelId
POST /api/channels/:channelId/agent/reset
POST /auth/logout

Local mode (AUTH_MODE=local) additionally registers these routes. It disables the authorization-code flow, so /auth/github and /auth/github/callback return 404; /auth/github/install and /auth/github/setup keep working:

POST /auth/device
GET  /auth/device
POST /auth/device/complete
POST /auth/device/consent
POST /auth/device/cancel

The repository-scoped document endpoint backs readable browser URLs. Existing UUID routes remain internal API and collaboration entry points.

API and authentication paths are owned by the server in development and production.

Live collaboration is multiplexed over /ws. External coding agents use the separate Streamable HTTP endpoint at /mcp; unlike the browser API, its caller-supplied bearer is independent of the GitHub App installation and can perform write-authorized document and implementation lifecycle operations.