Token refresh isn’t just a backend deal, it can make or break your app’s performance. Learn the trade-offs between four proven strategies and how to choose the right one for your stack.

Fenris uses the OAuth2 client credentials flow for authenticating client access to our services. The process is straightforward; you make a call to an authentication endpoint to obtain an access token to interact with APIs. 

However, that token expires in 24 hours, so managing these tokens efficiently is just as crucial as acquiring them. How and when tokens are refreshed can significantly impact the performance, scalability, and reliability of your application. In this blog post, we’ll explore several strategies for refreshing OAuth2 tokens, examining their pros, cons, and implementation nuances. 

Let’s explore four key strategies, each with differing trade-offs.

Note: one of the reasons we use industry standards like OAuth2 is that they are often supported “out of the box” by the common frameworks. So before diving into the options below, check to see if your framework already has you covered. 

Strategy 1: Refresh Every Time

This approach involves refreshing the token each time a request is sent to the API. It is perhaps the simplest implementation, making it ideal for developers looking to reduce complexity in their projects. In this approach, you simply call the authentication endpoint before each call to the Fenris API’s, supplying the new token in the request.

Advantages

• Ease of Implementation: Since the token is refreshed on every request, there’s no need to manage expiration or errors. 

Disadvantages

• Slower Performance: Making a token request before each API call introduces latency, as the token refresh process must complete before the actual request can be processed. In addition, it’s generally expected that the token request is rarely called, so the performance of a token endpoint is usually not optimized.
• Higher Resource Consumption: Frequent refreshes increase network usage, potentially affecting scalability and costs for your system.

Strategy 2: Refresh When the Call Fails

In this method, the token is refreshed only when an API request fails due to token expiration. The application recognizes the failure, refreshes the token, and retries the request. Once a token is created, it is made available to all requests. When a request returns a “401 – Not Authorized” response, then a new token is requested. The new token is made available to future requests, and the process repeats.

Advantages

• Reduced Frequency: Tokens are refreshed far less frequently compared to the "Refresh Every Time" method, saving network and server resources.

Disadvantages

• Slower Recovery: If a token fails, the application must refresh it and retry the request, introducing delays for that user.
• Multithreading Issues: In multi-threaded systems, simultaneous requests may fail due to an expired token, resulting in multiple threads attempting to refresh it at the same time. This approach should only be used if the client system is single-threaded or requests are spaced out in time.

Strategy 3: Check Expiration and Refresh

This approach involves proactively checking the token's expiration time before making an API request. If the token is about to expire, it is refreshed in advance. This is essentially the same approach as above, but it is a little bit leaner since it anticipates the expiration, saving a round trip.

Advantages

• Improved Efficiency: By avoiding failed requests, this strategy is slightly faster than waiting for the token to expire and handling failures.

Disadvantages

• Computing the expiration time can be tedious, as the timestamps in the token are in seconds since the epoch. There are utility routines and packages for most languages to make this easier.
• Multithreading Issues: Similar to "Refresh When Fails," this strategy can encounter race conditions where multiple threads check expiration and attempt to refresh the token simultaneously. The same caveats apply.

Strategy 4: Refresh in the Background

This is arguably the most efficient and robust approach to token refresh management. Here, a dedicated background thread or process handles token refreshes independently of API requests, ensuring that valid tokens are always available. Fenris tokens expire after 24 hours, so you can set up the refresh process to run every day at a set time.

Advantages

• Fast Request Handling: API requests proceed quickly because they always use a pre-refreshed token.
• No Multithreading Issues: Since a single thread or process is responsible for refreshing tokens, there’s no risk of race conditions or duplicate refresh attempts.

Disadvantages

• Added Complexity: Implementing a background refresh mechanism requires additional setup, including managing threads or processes and schedulers.
• Resource Allocation: Dedicated resources for background tasks may increase overhead, especially in resource-constrained environments.

Choosing the Right Strategy

The best strategy for refreshing OAuth2 tokens depends on the specific requirements of your application and its infrastructure. Here are a few considerations to help guide your decision:

• Low Complexity Projects: If simplicity is your goal, “Refresh Every Time” may be ideal, particularly for small-scale applications or prototypes.
• Resource Optimization: For applications requiring efficient resource usage, “Refresh When Fails” or “Check Expiration and Refresh” offers a balanced trade-off between performance and complexity.
• High-Performance Systems: If your application handles frequent API requests or operates in a multi-threaded environment, “Refresh in Background” is likely the best choice.

Implementation Tips

Regardless of the strategy you choose, here are some best practices to consider:

• Thread-Safe Techniques: Use synchronization mechanisms to address multi-threading issues. For example, employ mutexes or locks to prevent race conditions.
• Logging and Monitoring: Implement robust logging to track token refresh attempts and detect anomalies in the process.
• Leverage Frameworks: Many frameworks, such as Spring Security or OAuth libraries, offer built-in support for token refresh mechanisms. Utilize these tools to simplify your implementation.

Conclusion

Managing the Fenris token is a critical aspect of ensuring secure and efficient application performance. By understanding the trade-offs of different strategies—refreshing every time, on failure, checking expiration, or using background refresh—you can select the optimal approach for your use case. As you implement these strategies, keep scalability, performance, and thread safety in mind, leveraging frameworks and best practices to streamline the process.