What are the common errors and challenges when refreshing access tokens in OAuth?

1 Why refresh access tokens?

Access tokens are designed to expire after a certain period of time, usually an hour or less, to reduce the risk of unauthorized access and replay attacks. However, this also means that applications need to obtain new access tokens periodically to maintain access to the resources. This is where refresh tokens come in. Refresh tokens are long-lived credentials that can be used to request new access tokens without requiring user interaction or consent. Refresh tokens are usually issued along with access tokens when the user first authorizes the application.

2 How to refresh access tokens?

The process of refreshing access tokens varies depending on the OAuth flow and authorization server being used. Generally, you should check the expiration time of the access token and request a new one before it expires. This is done by sending a POST request to the token endpoint of the authorization server with grant_type=refresh_token, refresh_token=the refresh token, and optionally scope=the scope of the new access token. After parsing the response from the authorization server, extract the new access token, refresh token, and expiration time. Finally, store the new tokens securely and use them for future requests to the resource server.

3 What are the common errors?

When refreshing access tokens, there are a few potential errors that may occur. For example, an invalid or expired refresh token may be rejected by the authorization server with an invalid_grant error. This means you must obtain a new refresh token by requesting user authorization again. Additionally, an invalid or mismatched scope may be rejected with an invalid_scope error. To fix this, you must specify a valid scope that matches the user's consent or request a new scope through user authorization. Lastly, network or server errors may cause the request to fail, so it is important to handle the error gracefully and retry the request later.

4 How to handle errors?

When refreshing access tokens, it's important to utilize a few best practices and tips. For example, you should use a back-off strategy that increases the delay between retries exponentially or randomly. Additionally, you should refresh proactively a few minutes before the expiration time or use a background process or a cron job to refresh periodically. Furthermore, you should only refresh conditionally when you receive an invalid_token or expired_token error from the resource server. Lastly, it's essential to refresh securely using HTTPS, encryption, and secure storage mechanisms. Do not expose or store the refresh token in insecure locations or channels.

5 How to refresh scope?

Sometimes, you may need to refresh the scope of the access token, which is the set of permissions that the user has granted to the application. This can be necessary if you want to request additional or different permissions from the user based on their preferences or actions. To refresh the scope of the access token, you need to redirect the user to the authorization endpoint of the authorization server with the new scope parameter and obtain a new authorization code or access token. Then, if you are using the authorization code flow, you must send the new authorization code to the token endpoint of the authorization server and receive a new access token and refresh token with the new scope. Lastly, store and use the new access token and refresh token securely and discard the old ones.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?