JWT (JSON Web Token) is a widely used token-based authentication mechanism in web applications. In a JavaScript app, it’s important to handle token refreshing to ensure user sessions remain secure and uninterrupted. In this blog post, we will explore how to handle JWT token refreshing in a JavaScript app.

What is JWT Token Refreshing?

JWT tokens have an expiration time, after which they become invalid. To avoid the need for users to re-authenticate frequently, a token refreshing mechanism can be implemented. Token refreshing involves obtaining a new valid token from the server using an existing refresh token, which extends the user’s session without requiring them to provide their credentials again.

1. Checking Token Expiration

When handling JWT token refreshing, the first step is to check the expiration time of the current token. This can be done by decoding the token payload and checking the exp (expiration) claim. If the token is expired or close to expiry, we can proceed with refreshing the token.

function isTokenExpired(token) {
  const decodedToken = decodeJWT(token);
  const expirationTime = decodedToken.exp;
  const currentTime = Math.floor(Date.now() / 1000);

  return expirationTime <= currentTime;
}

In the above example, the isTokenExpired function checks if the token’s expiration time (UTC) is less than or equal to the current time. If it returns true, the token is expired or close to expiring.

2. Refreshing the Token

To refresh the token, we need to make an API call to the server with the refresh token. The server can then validate the refresh token and issue a new access token with an extended expiration time. Here is an example of how the token refreshing API call can be made using the fetch API.

function refreshToken(refreshToken) {
  return fetch('/refresh-token', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({ refreshToken })
  })
    .then(response => response.json())
    .then(data => data.accessToken);
}

In this example, we make a POST request to the /refresh-token endpoint with the refreshToken in the request body. The response from the server should include a new access token (accessToken) that can be used for further authenticated requests.

3. Handling Token Refreshing in App Lifecycle

To ensure a seamless user experience, token refreshing should be handled at strategic points in the app’s lifecycle. For example, you can check the token expiration in the following scenarios:

• When the user loads the app or refreshes the page
• Before making an authenticated API call
• In the background at regular intervals using timers

function checkTokenExpiration() {
  const token = localStorage.getItem('accessToken');

  if (isTokenExpired(token)) {
    const refreshToken = localStorage.getItem('refreshToken');

    refreshToken(refreshToken)
      .then(newAccessToken => {
        localStorage.setItem('accessToken', newAccessToken);
      })
      .catch(error => {
        // Handle token refreshing error
      });
  }
}

// Check token expiration on page load or app startup
checkTokenExpiration();

// Example: Making authenticated API call
function fetchData() {
  checkTokenExpiration();

  // Make API call with access token
  // ...
}

In the above example, the checkTokenExpiration function is called to check the token expiration before making any authenticated API call. If the token is expired, it tries to refresh the token using the refreshToken function we defined earlier.

Conclusion

JWT token refreshing is crucial for ensuring secure and uninterrupted user sessions in a JavaScript app. By implementing the steps described above - checking token expiration, refreshing the token, and handling token refreshing in the app’s lifecycle - you can maintain a smooth user experience while maintaining the security of your application.

#javascript #jwt #tokenrefreshing