CardDAV Sync

Rondo Club includes a built-in CardDAV server that allows you to sync your contacts with apps like Apple Contacts, Android Contacts (via DAVx5), Thunderbird, and other CardDAV-compatible applications.

Overview

CardDAV is an address book client/server protocol designed to allow users to access and share contact data on a server. It’s supported natively by Apple devices and can be added to Android and other platforms using third-party apps.

Setting Up CardDAV Sync

Step 1: Create an App Password

For security reasons, CardDAV uses WordPress Application Passwords instead of your main account password.

1. Log in to Rondo Club
2. Go to Settings
3. Find the CardDAV Sync section
4. Enter a name for your app password (e.g., “iPhone Contacts”)
5. Click Create Password
6. Copy the generated password immediately - it will only be shown once

Step 2: Get Your Connection Details

In the CardDAV Sync section of Settings, you’ll find:

• Server URL: The CardDAV server address
• Username: Your Rondo Club username

Step 3: Configure Your Device

Apple Contacts (macOS)

1. Open System Preferences → Internet Accounts
2. Click Add Other Account → CardDAV account
3. Enter:
   • Account Type: Manual
   • Username: Your Rondo Club username
   • Password: Your app password
   • Server Address: The server URL from Settings
4. Click Sign In

Apple Contacts (iOS/iPadOS)

1. Open Settings → Contacts → Accounts
2. Tap Add Account → Other → Add CardDAV Account
3. Enter:
   • Server: The server URL from Settings
   • Username: Your Rondo Club username
   • Password: Your app password
4. Tap Next

Android (using DAVx5)

1. Install DAVx5 from Google Play or F-Droid
2. Open DAVx5 and tap + to add a new account
3. Select Login with URL and user name
4. Enter:
   • Base URL: The server URL from Settings
   • User name: Your Rondo Club username
   • Password: Your app password
5. Tap Login
6. Select your address book to sync

Thunderbird

1. Install the TbSync add-on
2. Install the Provider for CalDAV & CardDAV add-on
3. Open Tools → TbSync (or Extras → TbSync on some systems)
4. Click Account actions → Add new account → CalDAV & CardDAV
5. Select Manual configuration
6. Enter:
   • Account name: Rondo Club (or any name you prefer)
   • User name: Your Rondo Club username
   • CardDAV server address: The server URL from Settings
7. Click Add account
8. Enter your app password when prompted
9. Select the address book to sync

Technical Details

URL Structure

Endpoint	URL
Server root	https://your-site.com/carddav/
Principal	https://your-site.com/carddav/principals/{username}/
Address book	https://your-site.com/carddav/addressbooks/{username}/contacts/

Authentication

• Method: HTTP Basic Authentication
• Username: Your Rondo Club username
• Password: A WordPress Application Password (not your main account password)

Sync Features

• Bidirectional sync: Changes made in Rondo Club appear in your devices, and vice versa
• Sync tokens: Efficient incremental sync - only changed contacts are transferred
• Conflict resolution: Most recent change wins

Supported Data

The following contact fields are synced:

• First name, infix (tussenvoegsel), last name, nickname
• Email addresses
• Phone numbers (mobile, work, home)
• Physical addresses (street, city, state/province, postal code, country)
• Team and job title (from current work history)
• Birthday (from person record)
• Profile photo
• URLs (website, LinkedIn, Twitter, etc.)

Data Access

• Each user only sees their own contacts
• CardDAV access respects the same permissions as the Rondo Club web interface
• Admins cannot access other users’ contacts via CardDAV

Security Best Practices

1. Use unique app passwords: Create a separate app password for each device
2. Revoke unused passwords: Remove app passwords for devices you no longer use
3. Use HTTPS: CardDAV connections should always use HTTPS (enforced by default)
4. Monitor usage: Check the “Last used” date to identify inactive app passwords

Troubleshooting

”Authentication failed”

• Verify you’re using an app password from Settings, not your main account password
• Check that the username matches your Rondo Club username exactly (case-sensitive)
• Ensure the server URL is correct and includes the full path
• WordPress 6.8+ uses BLAKE2b hashing for app passwords - ensure your site is updated

”Connection refused” or “Server not found”

• Verify the server URL is correct
• Check that your site is accessible and HTTPS is working
• Ensure no firewall is blocking the connection

Contacts not appearing

• Wait a few minutes for the initial sync to complete
• Check that you have contacts in Rondo Club
• Try forcing a sync in your CardDAV app

Sync conflicts

• The most recently modified version of a contact is kept
• If you edit the same contact on multiple devices simultaneously, changes from one device may be overwritten

Backend Implementation

The CardDAV server uses sabre/dav, a popular open-source WebDAV/CardDAV/CalDAV library. Key components:

• Authentication: WordPress Application Passwords verified via wp_verify_fast_hash() (WordPress 6.8+ BLAKE2b) with fallback to wp_check_password() for older versions
• Principal Backend: Maps WordPress users to DAV principals
• CardDAV Backend: CRUD operations on Person custom post type
• Sync Support: Change tracking with sync tokens for efficient updates

For more details, see the source code in includes/carddav/.