Passkeys Under the Hood: What's Actually Happening When You Use Face ID to Log In

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Every developer I know understands that passwords are broken. What fewer people have actually dug into is why passkeys fix this at the protocol level — and how surprisingly simple the WebAuthn API is to implement.

Here's the full picture: what's happening cryptographically, how the browser API works, and a quick comparison of the libraries worth using in production.

The Core Problem With Passwords (The Actual Technical One)

Passwords fail not because users pick weak ones. They fail because of how the authentication model works:

User creates a password
Server stores a hash of it
User sends the password on every login
Server hashes it and compares

Step 3 is the problem. The credential gets transmitted. That transmission can be intercepted (phishing), the hash can be cracked (breach), or the same credential works on other sites (credential stuffing). Every "password best practice" is mitigation, not a fix.

Passkeys change the model entirely.