I had this discussion in my workplace and wanted to share and get opinions from the folks here. (I suspect StackOverflow might not appreciate such open ended questions).
Context: We have a microservice involved in pricing signalling to our users. We have an endpoint which have the following:
- Input: an array of item ID’s
- Output: the expected final price of the given items.
The item prices are quite volatile (and no, it is not crypto related), and is dependent on things like instantaneous supply-demand, promotions, etc.
Since the prices change quite frequently, it became a requirement that we commit to the price that was shown to the user initially, up to a certain time period (eg 5 min after the price was calculated). This improves the UX since the user will be charged as according to what they expected at the start.
Currently, in our system, we achieve this via a JWT, which contains all the details in the request, the obligatory signature, and the expiry set to 5 min from the time it was generated.
After generating this receipt, the FE can then call the endpoint with the JWT which does the actual payment processing using the params encoded in the token. This way, we know that the params + the total cost that is quoted in the JWT originates from our service since we verify that we signed it.
And the system evolves once more. We see that in the system, there is this mechanism, that if the token is expired, we do not reject the request at the charging step. Instead, we call the price endpoint internally using the params provided, and check if the price is the same as in the expired JWT. If it is the same, we process it as normal despite the JWT being expired.
This is where the contention lies. I believe that we should force the user to procure another non-expired JWT and removing this complex logic while others believe in the value of this improved UX where the user doesn’t need to restart the whole flow again.
What do y’all think? Which way would y’all architect the endpoint? Or is there something fundamentally wrong with our design (maybe JWT is not the best suited for this use case)?
The frontend should inform the user (that the “price lock” time has expired) and refresh the price automatically. Then when they click submit there should always be a non-expired token. You should also be storing details of these tokens server-side so you can validate that it’s not been tampered with (if someone gets the private key. They can submit orders for any price?)
I think the idea was that if they managed to get the private key, we have away bigger problems on our hands than them submitting fraudulent orders. Even with server-side tokens, the same could happen if someone get access to your machine.