caldav-mcp-wrapper

A minimal, self-hosted MCP server that exposes read and write tools for a CalDAV calendar — designed for Apple iCloud (via an app-specific password), and compatible with any CalDAV server.

It is a CalDAV counterpart to smtp-mcp-wrapper and follows the same deployment and security model.

Tools

Read:

Write (disabled when READ_ONLY=true):

Times are ISO 8601. Use YYYY-MM-DD with all_day: true for whole-day events.

Related MCP server: Google Calendar MCP Server

Security architecture — read this first

This server implements no authentication of its own, by design. It MUST be gated by an authorization service. Do not expose it directly to the internet.

The intended topology keeps the server on an internal network only, with every external request flowing through an identity-aware proxy:

edge tunnel → reverse proxy (TLS) → Pomerium (SSO + allowlist to a single identity) → caldav-mcp-wrapper

Any equivalent identity-aware proxy works (Cloudflare Access, oauth2-proxy, etc.). docker-compose.yml deliberately publishes no host ports: the container is reachable only over the internal proxy network by container name.

Defense-in-depth beyond the proxy:

• Calendar allowlist — ALLOWED_CALENDARS hard-limits which calendars any tool can touch, so even a misused tool cannot reach other calendars.

• Read-only mode — READ_ONLY=true disables all write tools.

• Optional Pomerium identity verification — set REQUIRE_POMERIUM_IDENTITY=true to cryptographically verify Pomerium's identity assertion (signature + expiry + audience) on every /mcp request against Pomerium's JWKS. This blocks anything on the shared Docker network from bypassing Pomerium and reaching the app directly. When enabled, set pass_identity_headers: true on the Pomerium route and provide POMERIUM_JWKS_URL and POMERIUM_AUDIENCE.

iCloud setup

1. Sign in to account.apple.com → Sign-In and Security → App-Specific Passwords → generate one for this server.

2. Set CALDAV_USERNAME to your Apple ID email and CALDAV_PASSWORD to that app-specific password.

3. Leave CALDAV_URL at the default https://caldav.icloud.com/; the client discovers your calendars from there.

App-specific passwords require two-factor authentication on your Apple ID.

Configuration

All configuration is via environment variables — see .env.example for the full annotated list. Secrets are injected at runtime and never baked into the image. Key variables:

Run

cp .env.example .env      # fill in CALDAV_USERNAME / CALDAV_PASSWORD etc.
docker compose up -d

The image is built and published to GHCR by CI (ghcr.io/jb09/caldav-mcp-wrapper:latest).

Maintenance

• Dependabot opens weekly PRs for the Python deps, the Docker base image, and the GitHub Actions used in CI.

• CI (build workflow) builds the image on every push/PR, pushes to GHCR on main, and does a weekly no-cache rebuild so OS/Python security patches land even without code changes.

• Auto-merge (dependabot-automerge workflow) enables auto-merge for patch/minor Dependabot bumps once required checks pass; major bumps are left for manual review.

• Watchtower (opt-in label in compose) pulls refreshed images automatically.