The logout API is used to log out a user from a website or application. When a user logs in, they are typically assigned a session which keeps them logged in. The logout API provides a way to invalidate this session and log the user out.
How does the logout API work?
The logout API works by making a request to the server to invalidate the user’s current session. This is usually done by making a POST request to a logout endpoint. For example:
POST /logout
The server will then invalidate the session ID stored on the server side, effectively logging out the user. Any subsequent requests using that session ID will no longer be authorized.
Invalidating the session
On the server side, invalidating the session usually involves deleting the session data or resetting the session ID. Some common ways to invalidate a session include:
- Deleting the session record from the session store
- Regenerating a new session ID
- Setting the session expiration to 0
This ensures any session data for that user is cleaned up and future requests cannot be made using the same session.
Letting the client know
In addition to invalidating the session on the server, the logout API also needs to tell the client that the session is no longer valid. This is usually done by clearing any session cookies in the response:
HTTP/1.1 200 OK Set-Cookie: sessionId=; expires=Thu, 01 Jan 1970 00:00:00 GMT;
This clears the sessionId cookie and sets its expiration in the past. This tells the browser to remove this cookie, effectively logging out the user.
Why is the logout API needed?
Here are some reasons why the logout API is important:
Security
The logout API helps improve security by letting you invalidate sessions when no longer needed. This helps prevent against session hijacking or reuse of an abandoned session.
User experience
The logout button is a common part of most web UIs. The logout API gives you a way to implement this cleanly on the front and back end.
Multiple devices
When a user logs in on multiple devices, calling the logout API will log them out across all devices.
Session expiration
The logout API provides a way to actively expire a session, rather than waiting for a timeout.
When should you call the logout API?
Here are some common cases where you would call the logout API:
User clicks “Logout” button
When a user clicks a logout button in your UI, you need to call the logout API to invalidate their session.
Token expiration
If your application uses timed access tokens, you may want to call logout once the token expires.
Deleting a user account
When a user account is deleted, you should log out all associated sessions.
Suspicious activity
If you detect suspicious or unauthorized activity, you may want to forcibly log out the session.
How to call the logout API
To call the logout API, you’ll need to make a request from your frontend to the backend logout endpoint. Here is an example flow:
- User clicks logout button
- Frontend makes POST /logout API request
- Backend invalidates session and clears cookies
- Backend returns 200 OK response
- Frontend clears session data and redirects to login page
Frontend
On the frontend, you need to:
- Make POST request to /logout endpoint
- Clear session storage
- Remove cookies
- Redirect to login page
Backend
The backend needs to:
- Invalidate session
- Clear session cookie in response
- Return 200 OK
Example Code
Here is some example code for both the frontend and backend:
Frontend (JavaScript)
“`js
// Make logout request
const response = await fetch(‘/logout’, {
method: ‘POST’
});
// Clear session data
sessionStorage.clear();
// Redirect to login page
window.location.href = ‘/login’;
“`
Backend (Node.js/Express)
“`js
app.post(‘/logout’, (req, res) => {
// Destroy session
req.session.destroy(err => {
// Clear cookie
res.clearCookie(‘sessionCookie’);
// Redirect to login
res.redirect(‘/login’);
});
});
“`
This shows the basic flow – making a POST request, clearing session data, and redirecting on both the frontend and backend.
Common Pitfalls
Here are some common pitfalls to avoid when implementing logout:
Not clearing cookies
You must clear the session cookies on logout, or the user may stay logged in if they have the cookies cached.
Not destroying session
Make sure to destroy or invalidate the session on the backend. Simply redirecting may not fully log them out.
Access tokens not revoked
Make sure to revoke any OAuth access tokens or API keys on logout as well.
Old pages not refreshed
Refresh old tabs still open to your app after logging out to remove any cached auth.
Assuming logout is instant
Logout may take some time to propagate across devices. Don’t assume they’re logged out immediately.
Logging Out of Specific Services
When integrating with third-party services like social networks, you’ll want to log out of those services as well on logout. Here are some tips for some common ones:
Use the Facebook JavaScript SDK function FB.logout() to log out of Facebook. This will clear any Facebook cookies.
Call the Google signOut() method from the GoogleAuth library. This disconnects the Google account.
Call twttr.logout() to log out of Twitter and remove Twitter cookies.
SAML/SSO
For SAML/SSO providers, redirect users to the identity provider’s logout endpoint to log them out.
Conclusion
The logout API provides an important way for applications to securely log users out by invalidating their session. Key things to remember are:
- Make a POST request to /logout endpoint
- Clear session data on frontend and backend
- Remove auth cookies in the response
- Redirect to login page
- Revoke other tokens and log out of external services
Properly implementing logout improves security and gives users a way to cleanly exit your application across all their devices.