Best Practices for Receiving Webhooks
At Svix we often focus on sending webhooks, but let's not forget the crucial role of receiving webhooks. Let's delve into the best practices of ensuring security, verification, handling different sources and event types, and some other tips and tricks.
The first layer of securing your webhook receptions is verifying the signature. Most webhooks are secured via a webhook signature, and the responsibility lies on the reciever to ensure they verify this signature with the pre-shared key. It's simple, but absolutely crucial.
But what if someone manages to obtain a payload that was signed with the correct key and tries to re-transmit it to you? That's where protection from replay attacks comes in.
The first line of defense against this is a timestamp. Most webhook senders, including Svix, Stripe, and others, include a timestamp. The receiver's job is to ensure that the webhook was sent within a reasonable time frame, let's say within five minutes before or after the current time. This measure offers substantial protection against replay attacks.
If you use Svix libraries, the above steps are conveniently handled for you. You can read more about how Svix handles webhook signatures in our documentation.
Another crucial aspect for both security and operational integrity is idempotency. Implementations like Svix, among others, send a unique identifier in the header. What you should do as a receiver is store this identifier, perhaps in Redis or any other suitable environment, and use it to track whether you've already processed a message with that identifier. This step helps prevent handling the same message twice, either due to a replay attack or an integrity issue.
Handling Replay Attacks
Imagine your webhook is structured to add $100 to an account whenever a referral is made. In the absence of proper replay attack protection, an attacker can trigger the resending of the same event multiple times, resulting in multiple unwarranted credit transactions. This is why protection against replay attacks is vital.
Receiving from Different Sources
When dealing with different sources, it's best to treat them as distinct entities. Just as a GitHub API and a Stripe API aren't the same thing, neither are their webhooks. Therefore, have different URLs or paths for different webhooks. This not only ensures operational integrity but also simplifies log analysis and statistics.
Handling Different Event Types
Finally, when it comes to different event types from the same source, it's best to filter the event types on the sender side. This reduces the amount of noise hitting your endpoints and optimizes your operations. Then, internally, you can create a basic router to check the event types and send them to different handlers.
Receiving webhooks correctly is crucial, but as long as you have a robust sender that handles retries and so on, you can be a bit more flexible with some aspects. However, never compromise on security. Keep receiving those webhooks, and stay tuned for more tips and insights!