WebDAV Certificate Pinning & iOS API Modernization

[ppdms]

Implements certificate pinning for WebDAV servers with self-signed certificates using a Trust-On-First-Use (TOFU) security model.

Security Features

• ✅ Certificate pinning with byte-for-byte validation
• ✅ User trust prompts showing Common Name & SHA-256 fingerprint
• ✅ Certificate change detection (MITM protection)
• ✅ Expiration validation with user alerts
• ✅ Thread-safe implementation with NSLock protection
• ✅ 60-second timeout to prevent UI hangs

iOS Modernization

• Migrated deprecated UIButton APIs → Configuration API
• Migrated UIMenuController → UIMenu
• Updated AVURLAsset to async property loading
• Added @sendable conformance to URLSession delegates
• Fixed retain cycles in closure captures

Implementation Notes

• Certificates stored in UserDefaults (public data)
• Host validation ensures only WebDAV servers use custom trust
• Comprehensive inline documentation and test coverage

Testing

• Unit tests: WebDavCertificatePinningSpec
• Certificate storage/retrieval verified
• Trust flow and verification reset tested