When a user attempts to log in at facebook.com/login, the system processes identification in stages:
Facebook.com employs a multi-layered identification system to verify user identity during login. The process moves from user-supplied identifiers (email, phone, username) to credential validation (password) and finally to contextual verification (2FA, device recognition). This report outlines the primary identifiers accepted, the authentication flow, and the security protocols that protect against unauthorized access. Facebook.com Login Identify
Diagnostic checklist for users: