--- name: mcp-oauth-remote-gateway description: Manual OAuth for remote MCP servers on headless gateways. version: 1.0.0 author: Ben Barclay (benbarclay), Hermes Agent license: MIT platforms: [linux, macos] metadata: hermes: tags: [MCP, OAuth, PKCE, Remote-Deployment] related_skills: [native-mcp, mcporter, fastmcp] --- # MCP OAuth on a Remote Hermes Gateway ## Overview Hermes' built-in MCP OAuth client runs a one-shot HTTP listener on `127.0.0.1:` inside the Hermes process and registers that loopback address as the OAuth `redirect_uri`. That works perfectly for a local CLI on the user's own machine. It breaks completely when Hermes runs as a remote gateway (container, VPS, messaging bot), because the user's browser resolves `127.0.0.1` to the user's own laptop, not the remote container — so the authorization code never reaches Hermes. This skill does the OAuth dance by hand and writes the resulting tokens into the exact files Hermes' token storage expects, so a subsequent `/reload-mcp` finds cached tokens and skips the browser flow entirely. ## When to Use Use this skill when **all** of the following are true: 1. The user wants to add a remote HTTP MCP server that requires OAuth (not a static Bearer token). 2. Hermes is running as a **remote gateway** (container, VPS, Docker, managed service) — NOT a local CLI on the user's laptop. 3. The server supports OAuth 2.1 with PKCE and RFC 7591 Dynamic Client Registration (most modern MCP servers do — Better Stack, Linear, Cloudflare, Datadog, etc.). If it doesn't support DCR (GitHub is the notable exception), this skill does not apply — use a pre-registered OAuth App or a Personal Access Token instead. Do NOT use this for: - **Local CLI Hermes** — just set `auth: oauth` in `mcp_servers.` and `/reload-mcp`. The built-in flow opens a browser and captures the callback on localhost. Works perfectly. - **Servers that accept a static Bearer token (API key)** — always prefer `headers.Authorization: "Bearer "` when the user is willing. Simpler, no refresh dance. - **GitHub Copilot MCP** (`api.githubcopilot.com/mcp/`) — GitHub does not expose DCR. Use a PAT or a pre-registered OAuth App (see pitfall 12). ## Why the Built-in OAuth Flow Fails on a Remote Gateway Hermes' native MCP OAuth client (`tools/mcp_oauth.py`): 1. Picks a free local port `P`. 2. Registers a dynamic OAuth client with the AS, sending `redirect_uri = http://127.0.0.1:P/callback`. 3. Starts an HTTP server on `127.0.0.1:P` **inside the Hermes process**. 4. Prints the authorize URL and waits for the code at its local endpoint. When Hermes runs remotely, the `127.0.0.1` in the `redirect_uri` is the remote container's loopback, not the user's. After authorizing, the user's browser 302s to `http://127.0.0.1:P/callback?code=...`, which resolves to the user's own laptop and fails to connect. The callback never reaches the Hermes process, the flow times out, and `/reload-mcp` returns "No MCP tools available" with no detail. Symptoms to recognize: `[xdg-open] ` processes under the hermes user, an empty or missing tokens directory (`$HERMES_HOME/mcp-tokens/`), and a reload that responds without any "Added/Reconnected: X" line in `change_detail`. ## Cheap First Fallbacks: the Built-in Flow's Own Escape Hatches Before any manual token surgery, check whether the built-in flow's fallbacks already cover the deployment. When Hermes detects a remote session it prints two options alongside the authorize URL (`tools/mcp_oauth.py`): 1. **Paste-back** — on an interactive TTY, a stdin reader races the HTTP listener. The user authorizes, the browser fails to connect to `127.0.0.1:`, and they paste the full address-bar URL (`?code=...&state=...`) back at the prompt. Works for SSH'd-in CLI sessions. 2. **SSH port-forward** — `ssh -N -L :127.0.0.1: @` makes the redirect reach the remote listener normally. Both require an interactive terminal to the Hermes host. The rest of this skill is for when there is NO interactive TTY — Hermes running purely as a messaging gateway/bot where `/reload-mcp` triggers the flow with nobody at a prompt. ## Preferred Front Door: the Hermes Dashboard (try this BEFORE manual token surgery) A remote Hermes gateway often also runs the **dashboard** web UI as a SEPARATE process (e.g. `hermes dashboard --host 0.0.0.0 --port `; check with `ps aux | grep 'hermes dashboard'`). It exposes a connector/MCP console — endpoints like `/api/mcp/servers`, `/api/mcp/status`, and `/connectors` (all login-gated; a cookieless curl returning 401/302 confirms they exist). **Why the dashboard solves the core problem:** when the user drives OAuth from the dashboard *in their own browser*, the redirect lands in a context the dashboard can capture — sidestepping the `127.0.0.1`-callback failure that breaks the CLI/manual flow. So the correct escalation order for "add or re-auth an OAuth MCP server on a remote gateway" is: 1. **Dashboard, in the user's browser** — the intended front door. Add servers, run OAuth, reload, all authenticated as the user. No copy-paste-callback dance, no hand-writing token files. 2. **Manual token surgery (the rest of this skill)** — the FALLBACK for when there's no browser session to the dashboard (pure-chat/headless context). **Finding the dashboard's PUBLIC URL.** The dashboard binds internally to `0.0.0.0:`, but the user needs the externally-reachable URL. Most deploy platforms inject it into the environment — grep for it rather than making the user hunt: ```bash env | grep -iE "HERMES_DASHBOARD_PUBLIC_URL|RAILWAY_PUBLIC_DOMAIN|RAILWAY_STATIC_URL|RAILWAY_SERVICE_.*_URL|PUBLIC_URL|BASE_URL|DOMAIN" \ | sed -E 's/(TOKEN|SECRET|KEY|PASSWORD)=.*/\1=***REDACTED***/I' ``` `HERMES_DASHBOARD_PUBLIC_URL` is authoritative when present. On Railway also check `RAILWAY_PUBLIC_DOMAIN` / `RAILWAY_STATIC_URL` (the `*.up.railway.app` host) and `RAILWAY_SERVICE_*_URL` vars, which sometimes carry a friendlier custom domain. Hand the user the full `https://` URL and point them at the Connectors/MCP section. ALWAYS pipe through the `sed` redaction above — these env greps sit next to `*_TOKEN`/`*_SECRET` vars. **What the dashboard does NOT fix (still host-side / shell):** stdio servers that need shell auth state (a CLI `login` command whose credentials may not persist across restarts) and anything reading credentials from `$HERMES_HOME/.env`. Those are out of the dashboard's scope regardless. ## The Workaround Do the OAuth dance manually, then write the resulting tokens into the exact files Hermes' `HermesTokenStorage` would have written, so on `/reload-mcp` Hermes finds cached tokens and skips the browser flow entirely. Run the shell commands below through the `terminal` tool on the gateway host and do the Python steps (PKCE generation, token exchange, file writes) via `execute_code` or a `terminal` python3 invocation — file writes must happen in the SAME code block as the token exchange (see pitfall 16). ### 1. Confirm it's a remote gateway ```bash env | grep -iE "HERMES|RAILWAY|CONTAINER" echo "$DISPLAY $WAYLAND_DISPLAY $SSH_CLIENT" ``` No display + a remote indicator = remote gateway. `tools/mcp_oauth.py::_can_open_browser()` uses these same env vars, so if Hermes' own auto-detect says "headless", the built-in flow won't work. ### 2. Find HERMES_HOME and the config path ```bash HERMES_HOME=$(python3 -c 'from hermes_constants import get_hermes_home; print(get_hermes_home())') echo "config: $HERMES_HOME/config.yaml" echo "tokens: $HERMES_HOME/mcp-tokens/" ``` ### 3. Discover OAuth metadata from the MCP server MCP servers advertise their OAuth setup via RFC 9728 (OAuth 2.0 Protected Resource Metadata). The `WWW-Authenticate` header on a 401 tells you where to look: ```bash curl -sI https://mcp.example.com | grep -i www-authenticate # → Bearer realm="mcp", resource_metadata="https://mcp.example.com/.well-known/oauth-protected-resource" ``` **Not every server returns `WWW-Authenticate`.** Some return a bare `{"errors":["Unauthorized"]}` 401 with no auth-discovery hint. When that happens, probe well-known paths directly: ```bash for p in \ /.well-known/oauth-protected-resource \ /.well-known/oauth-authorization-server \ /.well-known/openid-configuration ; do echo "=== $p ===" curl -s -A "python-httpx/0.27" "https://mcp.example.com$p" | head -c 400; echo done ``` Fetch the resource metadata to get `authorization_servers`, then fetch the AS's `/.well-known/oauth-authorization-server` to get `authorization_endpoint`, `token_endpoint`, and `registration_endpoint`. Pitfall: many servers sit behind Cloudflare and 403 bare `urllib` user agents. Always set `User-Agent: python-httpx/0.27` (or similar) on requests in this flow. ### 4. Dynamic Client Registration (RFC 7591) POST to the `registration_endpoint` with: ```json { "client_name": "Hermes Agent (manual OAuth)", "redirect_uris": ["http://127.0.0.1:8765/callback"], "grant_types": ["authorization_code", "refresh_token"], "response_types": ["code"], "token_endpoint_auth_method": "none", "scope": "" } ``` Omit `scope` entirely if the AS's `scopes_supported` is empty — see step 5 pitfall. Use port `8765` (or any port — nothing will listen). `token_endpoint_auth_method: none` marks this as a public PKCE client. Save the returned `client_id`. ### 5. Build the authorize URL with PKCE Generate: - `code_verifier`: `secrets.token_urlsafe(64)[:128]` - `code_challenge`: `base64url(sha256(code_verifier))` (no padding) - `state`: `secrets.token_urlsafe(24)` Query params: `response_type=code`, `client_id`, `redirect_uri`, `code_challenge`, `code_challenge_method=S256`, `state`, plus `resource=` (RFC 8707 — many servers require this to bind the token to the specific MCP resource). Include `scope=` ONLY if the AS metadata's `scopes_supported` is a non-empty array AND/OR the resource metadata declares specific scopes. If `scopes_supported: []`, omit the `scope` parameter — the server grants its full default set on its own. Fabricating scope strings against an empty `scopes_supported` can cause `invalid_scope` errors on some ASes. **Stash `code_verifier` and `state` to disk** (e.g. `/tmp/.mcp-oauth-work/.json`, 0600 perms). You need them for step 7, possibly across multiple chat turns. ### 6. Give the user the authorize URL ``` Open this URL in your browser: After approving, your browser will try to load http://127.0.0.1:8765/callback and fail to connect — THAT'S EXPECTED. Just copy the entire URL from the address bar (it will contain ?code=...&state=...) and paste it back here. ``` ### 7. Exchange the code for tokens When the user pastes the callback URL: 1. Parse `code` and `state` from the query string. 2. **Verify `state` matches the stashed value** (CSRF check — do not skip). 3. POST `application/x-www-form-urlencoded` to the `token_endpoint`: - `grant_type=authorization_code` - `code=` - `redirect_uri=` - `client_id=` - `code_verifier=` - `resource=` (if the AS required it in step 5, include here too) 4. Response contains `access_token`, `refresh_token`, `token_type`, `expires_in`, `scope`. ### 8. Write tokens in Hermes' exact schema `tools/mcp_oauth.py::HermesTokenStorage` expects two files under `$HERMES_HOME/mcp-tokens/` (create dir with `0o700`, files with `0o600`): **`.json`** — the `OAuthToken` pydantic model: ```json { "access_token": "...", "token_type": "Bearer", "expires_in": 7200, "refresh_token": "...", "scope": "read write" } ``` **`.client.json`** — the `OAuthClientInformationFull` model: ```json { "client_id": "...", "redirect_uris": ["http://127.0.0.1:8765/callback"], "grant_types": ["authorization_code", "refresh_token"], "response_types": ["code"], "token_endpoint_auth_method": "none", "scope": "read write", "client_name": "..." } ``` Write each file via `json.dumps(..., indent=2)`. Sanitize the filename with `re.sub(r'[^\w\-]', '_', server_name)[:128]` — this matches `_safe_filename()` in Hermes' token storage. ### 9. Add the server to config.yaml ```yaml mcp_servers: : url: "https://mcp.example.com" auth: oauth timeout: 180 connect_timeout: 60 ``` ### 10. Smoke-test the token BEFORE asking the user to reload Manually POST an MCP `initialize` request to confirm the token works end-to-end — this catches scope misconfigurations, wrong `resource` values, and CF blocks before the user is confused by another "No MCP tools available" reload: ```python body = json.dumps({ "jsonrpc": "2.0", "id": 1, "method": "initialize", "params": { "protocolVersion": "2025-06-18", "capabilities": {}, "clientInfo": {"name": "hermes-debug", "version": "1.0"}, }, }).encode() # POST to the MCP URL with: # Authorization: Bearer # Accept: application/json, text/event-stream # Content-Type: application/json # MCP-Protocol-Version: 2025-06-18 # User-Agent: python-httpx/0.27 ``` Expect HTTP 200 with `Content-Type: text/event-stream` and a JSON-RPC result containing `serverInfo` and `capabilities`. **Do not use `urllib` with its default UA** — Cloudflare will 403 you even though Hermes (which uses httpx) will succeed. `scripts/diagnose-oauth-mcp.py` automates this smoke test. ### 11. Tell the user to run `/reload-mcp` On reload, Hermes sees `auth: oauth`, calls `HermesTokenStorage.get_tokens()`, finds your cached tokens, skips the browser flow, and registers `mcp__*` tools. Refresh happens automatically before `expires_in` elapses. ## Pitfalls & Lessons Learned 1. **Do not assume "headless" means "OAuth impossible."** The built-in flow works fine for local CLI; the issue is strictly remote deployments where the user's browser and the Hermes process are on different machines. Check the execution environment before claiming OAuth isn't an option. 2. **Read the source, not just the skill docs.** `tools/mcp_oauth.py` and the MCP config reference in `website/docs/` are the authoritative references. Grep the tree before telling the user a feature "doesn't exist." 3. **Cloudflare UA filter.** Many MCP/OAuth providers front their infra with Cloudflare, which 403s `python-urllib/*` user agents on metadata endpoints even though those endpoints are public. Set `User-Agent: python-httpx/0.27` (or any browser-like string) on every request in this flow. Hermes itself uses httpx, so this is never a problem in the real connection path. 4. **Include `resource` in both authorize and token requests.** RFC 8707 resource indicators are not optional for most modern MCP servers — they bind the issued token to the specific MCP resource URL. Leaving it out sometimes still works but may yield a token that later fails at the MCP server with a scope/audience error. 5. **Trailing slash matters.** Some servers advertise the resource as `https://mcp.example.com/` with a trailing slash and reject tokens issued against the no-slash variant. Copy the `resource` value verbatim from the `.well-known/oauth-protected-resource` response. 6. **`/reload-mcp` is silent on failure.** If the reload shows "No MCP tools available" with no `change_detail` line, a server is in config but failed to connect and no error bubbled up. Tail the error log, smoke-test the token directly with a manual `initialize` POST, and — if everything looks good — ask for a full process restart. 7. **Circuit breaker can survive `/reload-mcp`.** `tools/mcp_tool.py` keeps a module-level error-count dict with a small threshold. Once tripped (e.g. after token expiry produces several consecutive failures), the tool handler can short-circuit before calling the server, so no successful call resets the counter. Symptom: reload says "Reconnected: X" but subsequent calls still fail with "server unreachable" in the same conversation. Recovery order: try `/reload-mcp` FIRST (cheap, no chat-process blip) — on current builds it can clear the counter; only escalate to a full gateway process restart if a live call STILL short-circuits after reload. Do not lead with "you must restart." 8. **Refresh on an expired access_token + a tripped breaker is a deadlock.** The auto-refresh logic runs inside the MCP call path, which the breaker short-circuits once tripped. Manually refreshing the token on disk does not help by itself — pair a manual token refresh with a full restart, not a `/reload-mcp`. 9. **`invalid_grant` on a manual refresh means the refresh token is DEAD — re-auth is the only fix, do not loop.** When the access_token has been expired long enough, the refresh_token can also be revoked/expired server-side. A `grant_type=refresh_token` POST then returns HTTP 400 `{"error":"invalid_grant",...}` (wording varies: "Grant not found", "Token expired", "refresh token is invalid"). There is NO recovery from the gateway side. Hand back to the user with two options: (a) re-run the full manual OAuth dance (steps 3–10), or (b) if the provider offers a static personal API key, switch to that — no refresh/expiry cycle, more durable for an unattended remote gateway. Detect early: before any create/update operation against an OAuth MCP, check `expires_at` vs `time.time()`; if already expired, attempt the refresh first and surface `invalid_grant` immediately rather than failing mid-task. 10. **A successful refresh that STILL yields a rejected token = server-side SESSION revocation; only a fresh authorization_code flow fixes it.** Distinct from pitfall 9. The stored token file can look healthy (`expires_at` well out, refresh_token present), yet a live `initialize` POST returns `401 invalid_token` with a JSON-RPC body like `{"error":{"code":-32002,"message":"Session expired. Please re-authenticate."}}`. The `grant_type=refresh_token` POST may **succeed** (HTTP 200, new access_token) — yet the brand-new token gets the SAME `-32002`. The provider revoked the underlying MCP *session* server-side; the OAuth refresh chain re-mints credentials but cannot re-establish a revoked session. Decision rule when an OAuth MCP reports "not connected": (1) smoke-test the stored access_token with a manual `initialize` POST; (2) if `401 invalid_token`, attempt a refresh and smoke-test the NEW token; (3a) new token works → write it + restart to clear the breaker; (3b) new token STILL gets `-32002`/"Session expired" → stop, this is session revocation, hand the user the authorize URL for a full re-auth. `scripts/diagnose-oauth-mcp.py` automates steps 1–2 and prints which branch you're in. For an unattended gateway whose session keeps getting revoked, prefer a static Personal API key. See `references/stripe-mcp-oauth-revocation.md` for a worked example of a provider that revokes weekly. 11. **Client info file is NOT optional.** Hermes needs `.client.json` to know the `client_id` for refresh grants. Skipping it means the first refresh fails and the user has to re-auth — writing both files is the whole point of this skill. 12. **Never hand-type the redirect URL for the user to open.** Generate the authorize URL programmatically with `urllib.parse.urlencode()`. Spaces in scopes and special chars in `state` break string-concatenated URLs. 13. **Security: the stash file contains the `code_verifier`.** Delete `/tmp/.mcp-oauth-work/.json` immediately after successful token exchange. There's no reason to keep a proof-of-identity secret around once it's consumed. 14. **Write what the token endpoint actually returned.** The AS may grant a narrower (or wider) scope than requested. Write the `scope` from the token-exchange response to `.json`, not what you asked for in step 5. When `scopes_supported: []`, the explicit scope list you send IS authoritative both ways: some servers grant exactly what you list (pass narrow scopes for least-privilege, or enumerate the full set if the user needs everything), and some won't echo the granted scope back at registration time — only the token-exchange response is authoritative. 15. **OAuth tokens often double as Bearer tokens against the provider's public REST API.** The access_token in `.json` is frequently not "MCP-only" — `Authorization: Bearer ` against the provider's documented REST API succeeds whenever the corresponding resource scope was granted. This is the OAuth 2.0 spec, not a provider quirk. When the MCP server is read-only but you need a write operation, check whether the OAuth token can hit the provider's REST API directly before suggesting a separate API key. 16. **Secret redaction can mask tokens in tool output.** If secret redaction is enabled, tokens and long opaque strings render as `***` in tool-result output, so you cannot `print(response)` to keep the access_token visible across turns. Combined with single-use `code` values from authorization_code grants: if you print the token-exchange response, you may lose the token AND consume the code, forcing a restart with a fresh authorize URL. **Always write the access_token directly to its final destination file in the SAME code block that performs the token exchange.** If you must print for debugging, print only `len(access_token)`, `token_type`, `scope`, `expires_in` — never the secret. 17. **GitHub MCP (`api.githubcopilot.com/mcp/`) uses a pre-registered confidential OAuth App, not DCR + PKCE-public.** Its client info ships with a real `client_secret` and `token_endpoint_auth_method: client_secret_post`. The token-exchange POST to `https://github.com/login/oauth/access_token` must include `client_secret` as a form field alongside `client_id`, `code`, `code_verifier`, and `redirect_uri` (PKCE is still honored on top of the secret). The redirect URI is **fixed** in the OAuth App config — you cannot change it, so the manual listener-port trick doesn't apply; the user just lets the browser fail to connect on that port and pastes the address-bar URL back. ## What NOT to do - **Don't use `mcp-remote` as a fallback.** It runs an npx subprocess whose OAuth callback server ALSO sits on the remote container's localhost — same problem. `mcp-remote` only helps when the MCP client doesn't speak remote HTTP at all (Hermes does natively). - **Don't push "paste your API token and I'll add headers"** if the user explicitly asked for OAuth. Offer the static-token shortcut only after explaining why the native OAuth flow fails in remote deployments. Respect the user's choice to do the extra legwork for rotation-free, scope-limited access. - **Don't claim Hermes doesn't support a feature without reading the source.** Grep the source tree before making capability claims. ## Quick Reference Files - `scripts/diagnose-oauth-mcp.py` — re-runnable, read-only-by-default diagnostic. Given a server name, it smoke-tests the stored access_token, attempts a refresh, smoke-tests the new token, and prints exactly which recovery branch you're in (`TOKEN_OK` = breaker/restart, `REFRESH_FIXED` = persist+restart, `SESSION_REVOKED` = full re-auth, `REFRESH_DEAD` = full re-auth/API key). Pass `--write` to persist a working refreshed token atomically. Never prints secret values. **Run this FIRST when an OAuth MCP server reports "not connected"** — it encodes the pitfall 7/9/10 decision tree. - `references/stripe-mcp-oauth-revocation.md` — a worked example (Stripe) of a provider that revokes its OAuth session on a recurring basis, and the durable fix: switch to a static restricted API key. ## Related - `native-mcp` — general guide to configuring MCP in Hermes. Authoritative config reference lives there. - `mcporter` — the external CLI bridge, for ad-hoc MCP calls outside of Hermes' config.