Every application needs user registration and login. This article builds a complete authentication system — from storing passwords safely to handling failed login attempts. Never Store Passwords in Plain Text Store a one-way hash, not the password. BCrypt is the industry standard: @Bean public PasswordEncoder passwordEncoder() { return new BCryptPasswordEncoder(12); // cost factor 12 → ~250ms per hash on modern hardware // strong enough to slow down brute-force attacks } BCrypt properties: