Protect the login itself: strong hashed passwords, lockout and rate limiting, MFA, and well-managed tokens.
CSRF rides the victim's auto-sent cookie; stop it with an unguessable token and SameSite cookies.
Protect data at rest, in transit, and in logs: hash passwords, force TLS, and mask sensitive fields.
Never concatenate user input into SQL: bind it as a parameter so data can never become code.
SSRF makes your trusted server fetch attacker-chosen URLs: allowlist destinations and block internal and metadata addresses.
Grant the minimum permission needed so a compromise can do minimum damage.
Escape untrusted data on output so the browser shows it as text, never runs it as script.