Single Page Applications (SPAs) rely heavily on session management to provide a seamless and secure user experience. When you use Auth0 in a React app, the authentication process results in the issuance of tokens, which are then used to identify and authorize users during their session. Auth0 maintains user sessions by storing these tokens and validating them on each request that requires authentication. This allows your app to remember a user's authentication state even as they navigate between different routes or refresh the page, provided the session is still valid. The session persists until the token expires or the user logs out, at which point the user must authenticate again to regain access to protected resources.

When handling tokens in a React application, you have several storage options, each with its own security implications:

• Memory storage: tokens are kept in JavaScript variables that exist only while the page is loaded. This approach is safest against cross-site scripting (XSS) attacks because the tokens are never written to persistent storage, but users will be logged out if the page is refreshed or closed;
• localStorage: tokens are stored in the browser's localStorage, allowing them to persist across page reloads and browser sessions. However, localStorage is vulnerable to XSS attacks, as malicious scripts can potentially access these tokens;
• Cookies: cookies can be configured to be HTTP-only and Secure, meaning they cannot be accessed by JavaScript and are only sent over HTTPS connections. This makes cookies a safer option against XSS, but they can be susceptible to cross-site request forgery (CSRF) if not properly configured.

Choosing the right storage mechanism depends on your application's security requirements and user experience expectations. The safest approach is to use memory storage, but for many SPAs, cookies with proper security settings provide a good balance of security and usability.