Identity is always an issue in a decentralized systems. DNS can be used but not everybody owns a domain name. Ultimately if you want to keep your identity over a federated network you have to rely on an identity provider : Government issued, centralized platform that act as Id Provider (facebook, github, google, etc). I'm not aware of decentralized provider, maybe in a blockchain, there are a lot of writings on the topic: https://www.sciencedirect.com/science/article/abs/pii/S10848...