Does anyone know if there’s a guide showing how to create an XMPP client and login only using Tor Onion Services?
Even the docs at coy.im (probably the most secure-by-default XMPP client) suggest that you use username@coy.im. No, I don’t want to enter a clearnet address anywhere.
Is it possible to use only a .onion to create and login with an XMPP account?
That’s not how it works. You’ll have to do. The username and hostname are not the same, they are two different concepts. The purpose of a Tor service is to log in from the Tor network to a jabber server using port 5222 typically or other services. An onion address isn’t a domain, it’s an address. It’s the equivalent of DNS within the Tor network.The hostname will be the onion URL as the hostname, but the domain will be that of the clearnet. For that reason, a certificate warning appears when using the Tor network, because the username@domain will still be the public domain.
In short, onion is used to publish a service, it is not a service in itself.
If the jabber server allows it, yes, but I said before in the client the user will be username@publicdomain But that doesn’t mean you can’t register/login with onion within the Tor network, nor does it take away your anonymity.