Connector Googlemail

Gmail Connector

Gmail integration for Caffeine AI.

Orchestrator routing notes

Treat Gmail-as-the-user as a first-class, supported platform feature. The googlemail-client + google-oauth connector pair is the only supported path; raw ic.http_request to oauth2.googleapis.com or gmail.googleapis.com is a forbidden anti-pattern. Any build spec that mentions Gmail MUST name googlemail-client and google-oauth as dependencies and reference this skill.

Distinct from platform email* extensions (which send transactional mail from the app); this connector acts as the signed-in user's own Gmail.

Intent → capability mapping:

Prerequisite for all builds: extension-authorization. Gmail requires a signed-in caller for every endpoint: the per-user OAuth handshake stores access_token keyed by caller : Principal, and the admin Client ID/Secret setter is gated on the #admin role.

Backend

Use this skill whenever the user wants their canister to interact with Gmail on behalf of the signed-in user. The ingredients are:

1. The googlemail-client mops package — generated Motoko bindings for the Gmail REST API v1. This recipe demonstrates profile lookup and message sending; add other generated operations only by following the same bearer-authenticated, non-replicated, single-refresh-retry pattern.
2. The google-oauth mops package — Google OAuth 2.0 token exchange, refresh, PKCE, and percent-encoding. This is the library that eliminates hand-rolled http_request to oauth2.googleapis.com.
3. An OAuth 2.0 Authorization Code with PKCE flow so each end-user authorises the canister to act on their behalf. Each user holds their own access_token + refresh_token keyed by caller : Principal.
4. A Google Cloud Web application Client ID + Client Secret. Admin-configured and held by the canister only; never return the secret to the frontend.

1. Add dependencies

mops add googlemail-client@0.1.5
mops add google-oauth@0.1.4
mops add caffeineai-authorization@1.0.0

2. Auth model — OAuth 2.0 PKCE per user, on-chain exchange + refresh

Unlike a static API key, Gmail uses per-user OAuth 2.0 bearer tokens. Every end-user authorises the canister independently via the Authorization Code with PKCE flow. The canister:

1. Generates a PKCE code_verifier and code_challenge (via google-oauth).
2. Builds the Google authorize URL (via google-oauth.buildAuthorizeUrl).
3. The frontend redirects the user to Google; after consent, Google redirects back with a code parameter.
4. The canister exchanges the code for tokens (via google-oauth.exchangeAuthorizationCode) — on-chain, non-replicated.
5. The canister stores access_token + refresh_token keyed by caller.
6. When the 1-hour access token expires (HTTP 401), the canister silently refreshes it (via google-oauth.refreshAccessToken) and retries.

Google Cloud Console setup

1. Create a Google OAuth 2.0 Web application client.
2. Under Authorized redirect URIs, register the exact deployed callback: https://<app-domain>/connect/gmail. The URI passed to Google must match this value byte-for-byte, including its scheme, path, and trailing slash.
3. Enable only the Gmail scopes the app needs on the consent screen.
4. Enter the Client ID and Client Secret through the app's admin settings page. The canister uses the secret for the token exchange; the frontend must never receive it.

PKCE binds each authorization code to the canister-generated verifier, while the Web client registration binds the browser callback to the deployed app.

OAuth scopes

Request both gmail.send and gmail.readonly for a typical send+read app.

Storing tokens

The bearer never leaves the canister. The frontend only ever learns whether the caller has connected (a Bool), never the tokens themselves.

• A Map<Principal, GmailConnection> keyed by caller. Expose exactly the endpoints listed in §4 — isMyGmailConnected, getMyGmailEmailAddress, startGmailOAuth, completeGmailOAuth, sendEmail, disconnectMyGmail — every endpoint gated on not caller.isAnonymous(). Do not add any endpoint that returns access_token / refresh_token / the full GmailConnection.
• Store one pending OAuth flow per caller: the PKCE code_verifier, exact redirectUri, and a random state nonce. Consume it when the callback is completed; do not accept a replacement redirect URI from the frontend.

Google refresh tokens do NOT rotate

Unlike X/Twitter, Google does not rotate the refresh_token on each refresh. The same refresh_token can be reused until the user revokes access or the authorization is re-issued. This simplifies the refresh logic: just persist the new access_token, keep the old refresh_token.

3. is_replicated = ?false is REQUIRED

1. Security. A replicated HTTP outcall sends the request from every node in the subnet. Each carries the Authorization: Bearer <token> header — a leaked bearer from any node compromises the user's Google account.
2. Billing. Replicated outcalls produce N parallel API calls. The IC charges ~13× the cycles, and Google counts each toward quota.
3. Determinism. Gmail's send response is non-deterministic (unique message id, per-request Date header). Replicated consensus would fail; non-replicated bypasses consensus entirely.

→ Always: is_replicated = ?false on every Config.

4. Canonical layout

The default shape: admin Client ID/Secret + per-user OAuth. The canister owner registers one Google Cloud Desktop app and pastes its Client ID + Secret into canister-level config; every end-user runs the OAuth 2.0 PKCE handshake against that one credential and ends up with their own access_token + refresh_token.

The example spans four files:

• src/backend/main.mo — the actor: state + includes only.
• src/backend/mixins/gmail-config.mo — admin-gated Client ID + Secret.
• src/backend/mixins/gmail-messaging.mo — per-user OAuth + sendEmail.
• src/backend/lib/gmail.mo — googlemail-client + google-oauth glue.

import Map "mo:core/Map";
import Nat64 "mo:core/Nat64";
import Principal "mo:core/Principal";
import AccessControl "mo:caffeineai-authorization/access-control";
import MixinAuthorization "mo:caffeineai-authorization/MixinAuthorization";
import MixinGmailConfig "mixins/gmail-config";
import MixinGmailMessaging "mixins/gmail-messaging";
import LibGmail "lib/gmail";

actor {
  let accessControlState = AccessControl.initState();
  include MixinAuthorization(accessControlState, null);

  let gmailConfig = {
    var clientId : Text = "";
    var clientSecret : Text = "";
  };
  include MixinGmailConfig(accessControlState, gmailConfig);

  let gmailConnections : Map.Map<Principal, LibGmail.GmailConnection> = Map.empty();
  let pendingGmailFlows : Map.Map<Principal, LibGmail.PendingOAuth> = Map.empty();
  include MixinGmailMessaging(gmailConfig, gmailConnections, pendingGmailFlows);
};

import AccessControl "mo:caffeineai-authorization/access-control";
import Runtime "mo:core/Runtime";

mixin (
  accessControlState : AccessControl.AccessControlState,
  gmailConfig : { var clientId : Text; var clientSecret : Text },
) {
  public query func isGmailConfigured() : async Bool {
    gmailConfig.clientId.size() > 0;
  };

  public shared ({ caller }) func setGmailCredentials(clientId : Text, clientSecret : Text) : async () {
    if (not AccessControl.hasPermission(accessControlState, caller, #admin)) {
      Runtime.trap("Unauthorized: Only admins can set Gmail credentials");
    };
    gmailConfig.clientId := clientId;
    gmailConfig.clientSecret := clientSecret;
  };
};

import Map "mo:core/Map";
import Principal "mo:core/Principal";
import Runtime "mo:core/Runtime";
import LibGmail "../lib/gmail";

mixin (
  gmailConfig : { var clientId : Text; var clientSecret : Text },
  gmailConnections : Map.Map<Principal, LibGmail.GmailConnection>,
  pendingGmailFlows : Map.Map<Principal, LibGmail.PendingOAuth>,
) {
  public query ({ caller }) func isMyGmailConnected() : async Bool {
    Map.containsKey(gmailConnections, Principal.compare, caller);
  };

  public query ({ caller }) func getMyGmailEmailAddress() : async ?Text {
    if (caller.isAnonymous()) {
      Runtime.trap("Sign in to view your connected Gmail address");
    };
    switch (Map.get(gmailConnections, Principal.compare, caller)) {
      case (?connection) ?connection.emailAddress;
      case null null;
    };
  };

  public shared ({ caller }) func startGmailOAuth(redirectUri : Text) : async Text {
    if (caller.isAnonymous()) {
      Runtime.trap("Sign in to connect Gmail");
    };
    if (gmailConfig.clientId.size() == 0) {
      Runtime.trap("Gmail is not configured (admin must set credentials)");
    };
    await* LibGmail.startAuthorize(
      gmailConfig.clientId, redirectUri, caller, pendingGmailFlows,
    );
  };

  public shared ({ caller }) func completeGmailOAuth(code : Text, state : Text) : async () {
    if (caller.isAnonymous()) {
      Runtime.trap("Sign in to connect Gmail");
    };
    if (gmailConfig.clientId.size() == 0) {
      Runtime.trap("Gmail is not configured");
    };
    let ?pending = Map.get(pendingGmailFlows, Principal.compare, caller) else {
      Runtime.trap("No pending OAuth flow — call startGmailOAuth first");
    };
    if (state != pending.state) {
      Runtime.trap("OAuth state did not match the pending Gmail flow");
    };
    Map.remove(pendingGmailFlows, Principal.compare, caller);
    let connection = await* LibGmail.exchangeCode(
      gmailConfig.clientId, gmailConfig.clientSecret, code,
      pending.redirectUri, pending.codeVerifier,
    );
    Map.add(gmailConnections, Principal.compare, caller, connection);
  };

  public shared ({ caller }) func sendEmail(
    to : Text, subject : Text, body : Text,
  ) : async Text {
    if (caller.isAnonymous()) {
      Runtime.trap("Sign in to send email");
    };
    let ?connection = Map.get(gmailConnections, Principal.compare, caller) else {
      Runtime.trap("Connect your Gmail account first");
    };
    await* LibGmail.sendEmail(
      gmailConfig.clientId, gmailConfig.clientSecret, connection, caller,
      gmailConnections, to, subject, body,
    );
  };

  public shared ({ caller }) func disconnectMyGmail() : async () {
    if (caller.isAnonymous()) {
      Runtime.trap("Sign in to disconnect");
    };
    Map.remove(gmailConnections, Principal.compare, caller);
  };
};

import Map "mo:core/Map";
import Nat64 "mo:core/Nat64";
import Principal "mo:core/Principal";
import Text "mo:core/Text";
import Runtime "mo:core/Runtime";
import OAuth "mo:google-oauth/OAuth";
import { gmail_users_messages_send; gmail_users_getProfile } "mo:googlemail-client/Apis/UsersApi";
import { type Message; JSON = Message } "mo:googlemail-client/Models/Message";
import { defaultConfig; type Config } "mo:googlemail-client/Config";

module {
  public type GmailConnection = {
    accessToken : Text;
    refreshToken : Text;
    emailAddress : Text;
  };

  public type PendingOAuth = {
    codeVerifier : Text;
    redirectUri : Text;
    state : Text;
  };

  let SCOPES : Text = "https://www.googleapis.com/auth/gmail.send https://www.googleapis.com/auth/gmail.readonly";

  func configForToken(token : Text) : Config {
    {
      defaultConfig with
      auth = ?#bearer(token);
      is_replicated = ?false;
      max_response_bytes = ?Nat64.fromNat(2_000_000);
    };
  };

  public func startAuthorize(
    clientId : Text, redirectUri : Text, caller : Principal,
    pendingFlows : Map.Map<Principal, PendingOAuth>,
  ) : async* Text {
    let codeVerifier = await OAuth.generateCodeVerifier();
    let state = await OAuth.generateCodeVerifier();
    Map.add(pendingFlows, Principal.compare, caller, {
      codeVerifier;
      redirectUri;
      state;
    });
    OAuth.buildAuthorizeUrl(clientId, redirectUri, SCOPES, state, OAuth.computeCodeChallenge(codeVerifier));
  };

  public func exchangeCode(
    clientId : Text, clientSecret : Text, code : Text,
    redirectUri : Text, codeVerifier : Text,
  ) : async* GmailConnection {
    let tokens = await OAuth.exchangeAuthorizationCode(clientId, clientSecret, code, redirectUri, codeVerifier);
    let accessToken = accessTokenOf(tokens, "Token exchange");
    let refreshToken = switch (tokens.refreshToken) {
      case (?t) t;
      case null Runtime.trap("Token exchange failed: missing refresh_token");
    };
    let profile = try {
      await* gmail_users_getProfile(configForToken(accessToken), "me", #_1_, "", #json, "", "", "", "", true, "", "", "");
    } catch e {
      Runtime.trap("Failed to fetch Gmail profile: " # e.message());
    };
    let emailAddress = switch (profile.emailAddress) {
      case (?e) e;
      case null Runtime.trap("Gmail profile did not return an email address");
    };
    { accessToken; refreshToken; emailAddress };
  };

  /// Send an email. On HTTP 401, refreshes the access token once and retries.
  /// Persists the refreshed token into `gmailConnections` keyed by `caller`.
  public func sendEmail(
    clientId : Text, clientSecret : Text, connection : GmailConnection,
    caller : Principal, gmailConnections : Map.Map<Principal, GmailConnection>,
    to : Text, subject : Text, body : Text,
  ) : async* Text {
    let rawMessage = "To: " # to # "\r\n"
      # "Subject: " # subject # "\r\n"
      # "Content-Type: text/plain; charset=UTF-8\r\n\r\n" # body;
    let message : Message = { Message.init {} with raw = ?rawMessage.encodeUtf8() };
    try {
      messageIdOf(await* gmail_users_messages_send(
        configForToken(connection.accessToken), "me", #_1_, "", #json, "", "", "", "", true, "", "", "", message,
      ));
    } catch e {
      let msg = e.message();
      if (not (msg.contains(#text("401")) or msg.contains(#text("Unauthorized")))) {
        Runtime.trap("Gmail send failed: " # msg);
      };
      let refreshed = await OAuth.refreshAccessToken(clientId, clientSecret, connection.refreshToken);
      let newToken = accessTokenOf(refreshed, "Token refresh");
      Map.add(gmailConnections, Principal.compare, caller, {
        connection with accessToken = newToken;
      });
      messageIdOf(await* gmail_users_messages_send(
        configForToken(newToken), "me", #_1_, "", #json, "", "", "", "", true, "", "", "", message,
      ));
    };
  };

  func accessTokenOf(tokens : OAuth.TokenResponse, operation : Text) : Text {
    switch (tokens.error) {
      case (?error) {
        let description = switch (tokens.errorDescription) {
          case (?value) ": " # value;
          case null "";
        };
        Runtime.trap(operation # " failed: " # error # description);
      };
      case null {};
    };
    switch (tokens.accessToken) {
      case (?token) token;
      case null Runtime.trap(operation # " failed: missing access_token");
    };
  };

  func messageIdOf(result : Message) : Text = switch (result.id) {
    case (?id) id;
    case null "";
  };
};

5. Available API surface

google-oauth (OAuth 2.0 mechanics)

googlemail-client (Gmail REST API)

The canonical actor above intentionally implements only profile lookup and message sending. For another generated operation, keep bearer authentication and is_replicated = ?false, then apply the same single-refresh-retry pattern as sendEmail.

6. Cycles and response sizes

The google-oauth library uses Call.httpRequest from mo:ic/Call, which auto-computes and attaches the exact required cycles via the ic0.cost_http_request system API. No manual cycle budgeting is needed for token exchange or refresh calls.

For googlemail-client calls, defaultConfig.cycles = 30_000_000_000 (30B). A typical send costs ~10–15B cycles. Bump to 60B for large messages. Set max_response_bytes = ?2_000_000 for message reads that may include large payloads.

7. Things that will bite you

• is_replicated = ?false — see §3. Non-negotiable.
• Google refresh tokens do NOT rotate. Unlike X/Twitter, Google does not issue a new refresh_token on each refresh. Keep the original refresh_token and only persist the new access_token. The sendEmail function in §4 handles this.
• Access tokens expire in 1 hour. The sendEmail function catches HTTP 401, silently refreshes via google-oauth.refreshAccessToken, and retries once. If the refresh also fails, surface "re-connect your account".
• Callback URI exact-match. Every character (trailing slash, query string, port) must match between the authorize URL and the redirect. Google returns redirect_uri_mismatch otherwise. Always use window.location.origin + window.location.pathname for redirectUri and register that exact URI on the Google Web client.
• RFC 5322 raw Blob. Pass the message as a plain Blob in the raw field (?Text.encodeUtf8(mime)). The googlemail-client base64-encodes it for the API — do not base64-encode it yourself (that double-encodes and Gmail rejects it).
• HTTP 429 rate-limit. Surface the error to the caller; never silently retry inside the canister — a send retry may deliver duplicates.
• Don't expose the access token. gmailConnections is read only by Map.get(gmailConnections, ..., caller) inside sendEmail. No getMyGmailConnection, no getMyAccessToken, no iterator. A leaked bearer is a per-user account compromise.
• xgafv = #_1_, alt = #json for all Gmail API v1 calls. Leave optional string parameters "" and prettyPrint = false.
• userId = "me" refers to the authenticated user.

Frontend

Every build using this skill must ship:

1. A login flow — required. Gmail cannot work without a non-anonymous caller; the per-user OAuth handshake stores tokens keyed by caller : Principal, and the admin credential setter gates on #admin. The login flow comes from extension-authorization: useInternetIdentity, login/logout buttons, the useActor plumbing that injects the authenticated identity into every backend call.

2. An admin settings page — /settings/gmail (admin-gated):

   • Two password-inputs bound to setGmailCredentials(clientId, clientSecret). Submit on enter; clear inputs on success.
   • Status indicator driven by isGmailConfigured() (returns Bool). Show "Configured" / "Not configured" — never display the credentials.
   • Hide from non-admins via extension-authorization's isCallerAdmin query — non-admins should not see the link in the nav.

3. A "Connect Gmail" page — /connect/gmail (any signed-in user):

   • "Connect Gmail" button bound to startGmailOAuth(window.location.origin + window.location.pathname). Redirect the browser to the URL returned by the canister. Register this exact URI in the Google Cloud Console first.
   • On the return leg, read error, code, and state from URLSearchParams. If error is present, show the failed/declined connection state and do not call the canister. Only when both code and state are present, call completeGmailOAuth(code, state).
   • After either terminal path, call history.replaceState to remove the OAuth query parameters. This prevents a page refresh from reusing a one-time authorization code.
   • Status driven by isMyGmailConnected() (returns Bool). When connected, call getMyGmailEmailAddress() to show "Connected as user@email.com". This returns only the stored email address, never either bearer token.
   • Optional "Disconnect Gmail" button bound to disconnectMyGmail().

4. Empty-state nudge on the send-email UI — when isMyGmailConnected() is false, render an inline "Connect Gmail to send" link to /connect/gmail.

Suggested route layout:

/                   →  Main UI (any signed-in user; empty-state when no Gmail connection)
/settings/gmail     →  Admin credential config (admin-only)
/connect/gmail      →  Per-user OAuth handshake (any signed-in user)

Common to all variants

• Sign-in is required for every Gmail-related route. Wire the /settings/... and /connect/gmail routes through extension-authorization's auth guard (useInternetIdentity + redirect when !isAuthenticated).
• The frontend never persists tokens. No localStorage, no IndexedDB, no cookies — the canister mediates everything. The browser only ever sees Bool status flags and the OAuth redirect URLs.
• The OAuth state parameter is canister-generated and validated. The canister stores a random nonce with the pending verifier and callback URI. The frontend must pass both code and state to completeGmailOAuth; it never creates or modifies either value.
• The send-email UI itself is trivial: inputs for to, subject, body, a submit button. No client-side Gmail SDK, no token handling, no JSON serialization — the canister is the Gmail client.

Related

• mops add googlemail-client@0.1.5 — Gmail REST API bindings.
• mops add google-oauth@0.1.4 — Google OAuth 2.0 library (token exchange, refresh, PKCE).
• Google OAuth 2.0 for Web Server Applications — Web-client redirect URI and authorization-code flow reference.
• Gmail API v1 reference — what googlemail-client wraps.
• RFC 7636 — Proof Key for Code Exchange — PKCE spec.
• extension-authorization — required prerequisite. Provides Internet Identity login, useInternetIdentity / useActor frontend plumbing, and the #admin role gate.