Bluesky accounts are key pairs and DIDs but they keys are stored on a PDS server which handles signing. You own your keys and can migrate to a different server, but use a username (domain name actually) and password to login. This is similar to nsec bunker in many ways.
Discussion
Unfortunately i can't sign up for bluesky because I don't have an email address or birthdate.
Hows bluesky diff than Mastadon ? I found mastadon very difficult to use and bluesky sounds similar to me.
Different protocols. Bluesky is closer to nostr in that you control your identity and can choose what servers host your data. Right now bluesky data and ux is much closer to mastodon and twitter. Neither support encryption and private messages / groups or the more interesting new / different applications.