Currently, relying on tech companies for your universal login is the only option, but with open-source protocols like Lightning and Nostr, you have new options. Lightning allows you to log in using your LSAT and Macaroon to authenticate your account, but it has limitations.
Login with Lightning requires access to remote keys, and logging in with Nostr requires access to local keys, ideally stored in a browser extension. Now if your Lightning node goes down or you lose your connection, you also can’t auth with any service. If you’re using a custodial wallet or third-party service like an LSP, you’re trusting their node and basically moving your security and privacy assumptions to another custody provider.
Lightning pubkeys contain sensitive information and can leak confidential financial information, which is something many would not feel comfortable with and would prefer to keep their financial activity and other activity separate. Nostr public keys are safe to share with anyone as they are not tied to your Bitcoin activity.
Authorising with Nostr shares a real social identity with the service; applications can query your Nostr social graph, which is useful to show users you already know using a new service and provide you with a richer experience and limit spam.
A Lightning node is also not an exact identity but a unique identifier. It just tells you the person that authorises is the same random person that authed last time; it doesn’t tell you who they are.
A nostr pubkey is an identity. It tells a provider who you are, your name, what they look like, who they know, how you can pay them, and how you can message them. This is much more useful as an identity layer for an application. The application can show their profile picture and username, send secure cross-platform push notifications via NIP-04 encrypted Nostr DMs, etc.
Enabling Nostr-Auth applications can use it as part of talking to the broader nostr infrastructure, like the relays, or simply as a signal that this is an honest account and provide access to the specific service.