Tag: aspnetcore

You can use passkeys as a second factor after password login in ASP.NET Core Identity on .NET 10. Register a two-factor token provider for users who have a passkey, then add two endpoints: one creates passkey request options for the user who passed the password check, and the other verifies the passkey before completing sign-in. Store the user id from the password step in a short-lived cookie, and compare it with the passkey’s user before signing in.

A session cookie is a bearer token, which is a polite way of saying that whoever holds it is you. Copy the cookie, replay it from another machine, and the server happily serves your account. Nothing about the request proves which device it came from, so a cookie lifted by malware, an XSS payload, or a stray database backup keeps working until it expires. For a long-lived session, that can be weeks.