Letting people log in means proving who they are and then remembering it safely for the length of a visit. Both halves have well-known ways of going wrong.
Your options
- Email and password. The classic. You are responsible for storing passwords properly and for resets.
- Sign in with an existing account from a large provider. Fewer passwords for you to protect, but you depend on the provider and not everyone has or wants one.
- Magic links or one-time codes sent by email. No password, but email access becomes the key.
- A hosted authentication service. Outsourced, with its own cost and dependency.
What to get right whichever you pick
- Never store passwords in plain form. Use a slow, purpose-built password hashing algorithm; OWASP publishes current guidance.
- Rate-limit login attempts so passwords cannot be guessed at speed.
- Make password reset safe: single-use, expiring links that do not reveal whether an account exists.
- Use secure session cookies, and end sessions on logout.
- Offer two-factor authentication for anything valuable.
Why not roll your own
Small details, such as comparing values in constant time or invalidating old sessions, are easy to miss and invisible until exploited. A mature framework or library has already made those mistakes and fixed them.