When building an app that uses OAuth 2.0, using refresh tokens is essential to balance security and user experience. Refresh tokens are issued alongside access tokens during the initial login flow and typically live longer than access tokens, usually days or weeks. They can be used to obtain a new access token when the original one expires, allowing users to stay signed in without re-authenticating. However, if not handled properly, refresh tokens can become vulnerable to attacks, such as replay attacks. To mitigate this risk, it's crucial to store them securely, rotate them regularly, set expiration and revocation logic, and avoid using long-lived JWTs as refresh tokens. Misunderstanding "silent authentication" in SPAs, not rotating refresh tokens, and storing tokens in insecure methods can lead to security issues. By following best practices and understanding how to manage refresh tokens, developers can build trustworthy and secure auth flows that balance user experience with security.