Cross-Platform Calendar App Development

Proprietary calendar / Thebox® API integration My part will be a proprietary REST API from Thebox®. The mobile app must allow configuration of an API endpoint, username and password. These credentials must be stored securely using the operating system’s secure storage mechanism, such as Keychain on iOS and Keystore/Secure Storage on Android. After the first configuration, the app should authenticate automatically and sync with the Thebox® calendar without requiring the user to log in again every time. The Thebox® API will include: • An endpoint to receive/send all calendar events. • Full event information, including title, description, location, start/end date, timezone, recurrence rules, attendees, status, reminders, and metadata. • A route to retrieve Thebox® users, so the app can invite internal company users to an event. • A dedicated account/permission model for creating new events in the Thebox® calendar through the API. • Support for updating and deleting events where applicable. • Event identifiers or external reference fields to prevent duplicates when syncing with Google, Outlook, Apple Calendar, or Android Calendar. The app must map external calendar events into the Thebox® calendar format and keep enough metadata to know the original source of each event. For example: • Event created in Outlook → appears in the mobile app and is sent to Thebox®. • Event created in Google Calendar → appears in the mobile app and is sent to Thebox®. • Event created in iOS/Android local calendar → appears in the mobile app and is sent to Thebox® where platform permissions allow it. • Event created directly in the app → can be written to Thebox® and, depending on the selected source, optionally written back to the external calendar. The developer must clearly explain how they will handle: • Secure credential storage. • Automatic login/session renewal. • Event sync between external calendars and Thebox®. • Recurring events. • Attendees and Thebox® user invitations. • Duplicate prevention. • Conflict resolution. • Offline creation/editing and later synchronization. • Logs or sync status so users know whether an event was successfully delivered to Thebox®. Please note that the Thebox® API is the central company calendar. I will provide the REST API documentation, endpoint, test credentials, event structure, user route, and event creation route. In your proposal, please explain how you would structure the sync engine between Google Calendar, Microsoft Outlook, Apple/iOS Calendar, Android Calendar, and the Thebox® API.