What is interesting is that it is possible to open the keychain (SecKeychainOpen returns 0), but when trying to write to it, it fails with the same 100001 code. &#9;&#9;&#9;&#9;&#9;&#9;let path = "~/Library/Keychains/login.keychain-db"             var keychain: SecKeychain?             var status = SecKeychainOpen(path, &keychain)             log.warning("SecKeychainOpen \(status)")             let addErr = SecItemAdd([                     kSecClass: kSecClassGenericPassword,                     kSecAttrService: "aTestTestTest",                     kSecAttrAccount: "mrgumby",                     kSecUseKeychain: keychain,                     kSecValueData: "opendoor".data(using: .utf8)!                     ] as NSDictionary, nil)             if addErr != errSecSuccess {                 log.warning("Keychain SecItemAdd failed, error: \(addErr)")             } else {                 log.warning("Keychain success")             } result: SecKeychainOpen 0 Keychain SecItemAdd failed, error: 100001 Adding <key>com.apple.security.temporary-exception.files.home-relative-path.read-write</key> <array> <string>/Library/Keychains/login.keychain-db</string> </array> To extension entitlements doesn't help.

I have tried that, and when extension wants to write to the keychain, it always gets error 100001. A little more info and code example in another thread: https://developer.apple.com/forums/thread/672456?login=true&page=1#660300022