OAuth and service accounts solve different problems
OAuth is the right default when an individual wants an AI assistant to manage their own calendar. A service account is better when a team needs controlled access to shared calendars, room calendars, or workspace automation that should not depend on one person's login session.
Use OAuth for personal assistants
If Claude, OpenClaw, Cursor, or another MCP client is helping one person with their own schedule, OAuth keeps consent clear. The user connects their calendar, sees the requested scopes, and can revoke access later.
Use service accounts for shared operations
Service accounts make sense when the calendar is operational rather than personal: sales demos, on-call rotations, conference rooms, team holds, or a shared recruiting calendar.
One important limitation: creating calendars
CalendarMCP's create_calendar tool is OAuth-only. A service account can create calendars in Google, but those calendars would be owned by the service account, not by the user. For service-account setups, create the calendar in Google Calendar first, share it with the CalendarMCP service account, then add it from the dashboard.
The security checklist
- Grant the service account only the specific calendars it needs.
- Prefer read-only access until writes are required.
- Log every write action with the triggering user or task.
- Test create, update, and delete behavior before exposing the tool.
- Rotate credentials if the agent environment changes.
CalendarMCP's rule of thumb
Start with OAuth for personal calendar agents. Reach for service accounts when the calendar belongs to a workflow, a team, or a workspace resource.