What is the difference between addFilterBefore(), addFilterAfter(), and addFilterAt()?

All three register a custom Filter at a specific position relative to an existing named filter class in the chain. addFilterBefore() runs your filter earlier than the reference filter, addFilterAfter() runs it later, and addFilterAt() places it at the same logical position (commonly used to insert a custom token-validation filter where UsernamePasswordAuthenticationFilter would normally sit).