What validations should be applied to signup and login forms?

What validations should be applied to signup and login forms?

Signup and login forms should validate the expected shape and meaning of submitted data while giving users understandable feedback. Browser validation improves the experience, but the server must independently enforce the rules because requests can bypass the interface.

Define an explicit input contract

Specify required fields, expected types, and sensible length limits. An email value should be a string with an acceptable format, and a display name should fit the application's storage and interface constraints. Reject unexpected fields rather than allowing a signup request to assign its own privileged role.

Validation should cover syntax and business meaning on the server, even when the browser performs the same checks. OWASP input-validation guidance.

Keep email normalization consistent with the chosen account policy. Enforce account uniqueness at the database level as well as handling duplicate requests gracefully; two nearly simultaneous submissions should not create two accounts for the same normalized identity.

Handle passwords without changing their meaning

Apply the approved password policy during signup, allow password-manager use, and avoid silently trimming or truncating the submitted password. Login must verify existing credentials rather than reject an established account solely because a newer signup policy changed.

Do not place raw request objects directly into database queries. Extract validated scalar fields and use the database driver's intended query patterns. Keep user-submitted role or wedding identifiers separate from server-established ownership.

Make validation failures recoverable

For wedding-app onboarding, associate errors with the relevant fields and preserve safe input when a request fails. Indicate submission progress and prevent accidental duplicate actions without making the server depend on a disabled button.

Test missing fields, malformed types, excessively long values, duplicate signup attempts, and network failures. Also check keyboard navigation and readable error announcements. Distinguish field-format feedback from account lookup errors so helpful validation does not accidentally disclose whether a particular email is registered.