Federated account?

I was wondering, did I miss the federated authentication service? When a user has a mastadon account on one of the federated services, it is possible to follow and post on mastodon, react on lemmy and follow lemmy users, but creating a lemmy post isn't possible. When a user has a lemmy account, interaction with mastodon is possible, but to follow you need a mastodon account.

Isn't there an authentication service, so you can create user@fediverse.domain and interact wuth all services?