You can't do this with bitcoin core since it uses hardened derivation so you can't derive addresses using the extended public key. You should use electrum for this instead. An electrum watch-only wallet can mirror the addresses of a an electrum seeded wallet. So just create an electrum wallet on your desktop as normal and then grab the master public key aka extended public key via wallet menu > information. You can then derive addresses using that. The easiest way would be to install electrum on the server, restore the wallet using the xpub:
electrum restore xpub...
Then you can use the addrequest command with the --force switch to generate addresses:
electrum addrequest --force 0.1
The JSON code that is output will contain a unique address everytime. Note you may have to increase the gap limit on the seeded wallet on your desktop via
wallet.change_gap_limit(200) on the console tab (view > show console).
Electrum also has a JSON RPC interface as well but you will have to research how to use that yourself.