Two questions, two controls
Authentication answers, “Who is making this request?” Authorization answers, “Is this identity allowed to perform this action on this resource?” A user may be authenticated but still lack permission to delete a record or view another person’s private data. Treating these concerns separately makes access rules easier to reason about.
For example, a project application may allow signed-in users to read public project descriptions, while only the owner can edit a project and an administrator can manage accounts. The server must enforce these rules for every relevant request.
Apply least privilege
Least privilege means granting only the access a user needs. Roles can group permissions, but a role check alone may not answer resource-specific questions such as whether the current user owns a particular record. Check access at the appropriate boundary and keep the rule close to the operation it protects.
Hiding or disabling a React button can make the interface clearer, but users can call an API directly. Therefore, frontend visibility is not a substitute for backend authorization. Denied requests should return a suitable response without leaking sensitive details.
Validate inputs and protect configuration
Validate all incoming data on the server, even when the browser already checks it. Use framework-supported approaches for password storage, session management and token handling; do not invent cryptographic formats. Keep database passwords, signing keys and API secrets outside source code and frontend bundles.
Configure cross-origin access narrowly for the origins the application needs. Avoid logging passwords, tokens or unnecessary personal information. Error messages should help a legitimate user recover without exposing stack traces or internal configuration.
Test both allowed and denied access
Security tests should prove not only that an authorized action succeeds, but also that an unauthenticated request and an authenticated user without the required permission are rejected. Include attempts to access another user’s record if the application has ownership rules. These negative tests catch common gaps that happy-path tests miss.
Keep dependencies and framework configuration maintained, and review security behavior when authentication changes. AI-generated snippets may omit important controls; check official framework guidance, inspect the result and test it. Never share real credentials or private data with unapproved tools.
Security is part of feature design
Decide what data is sensitive, who should access it and how long it should be retained while designing the feature—not after it is built. Document assumptions and limitations. A clear threat boundary and a small set of tested permissions are more dependable than adding security annotations without understanding their effect.