Support .onion-addresses
I would like to put forward the request that gnome-online-accounts would support .onion-addresses a.k.a. tor hidden services.
I have a Nextcloud server that I run as a hidden service, unfortunately it isn't possible to integrate the cardDav and calDav services from it to the Gnome desktop because GOA doesn't support .onion-addresses. Unlike the webDav service that I connect to via Nextcloud-destop-sync-client, because it has its own proxy configuration, so I can tell it to go through localhost:9050 (default port for local tor service)
Now, instead of giving GOA its own proxy configuration it might make more sense to introduce a new type of proxy configuration to Settings - Network - Network Proxy. Let's call it .onion-address proxy and default value localhost:9050. So that when ever a Gnome application is given an .onion-address it will go through that proxy.