◇ Could this help me?
Yes. All five are well-established, safe authentication best practices that align with OWASP guidance: server-side validation, rate limiting and lockouts, password hashing, generic account-enumeration-safe error messages, and delegating auth to a vetted provider all reduce real attack surface. This is general security best practice worth adopting on any app that handles logins, not a project-specific tweak, and it improves safety rather than introducing risk.
You are helping build the login and authentication flow for an app. Apply these security best practices and explain each change as you make it: 1) validate and sanitize all user input on the server for every field; 2) add rate limiting and account lockouts to stop brute-force attempts; 3) never store passwords in plain text, hash them with a strong, modern algorithm; 4) return generic error messages such as "incorrect email or password" so attackers cannot tell which accounts exist; 5) recommend a trusted, well-maintained authentication provider instead of a custom implementation. For the provider, first research the specific option, what it is, how it works, who maintains it, and whether it is reputable, present those findings, and integrate or install it only after explicit approval.