Add support for cost param

[marceloverdijk]

It would be nice to have cost param like:

app.use(
  rateLimiter({
    windowMs: 15 * 60 * 1000, // 15 minutes
    limit: 100, // Limit each IP to 100 requests per `window` (here, per 15 minutes).
    standardHeaders: "draft-6", // draft-6: `RateLimit-*` headers; draft-7: combined `RateLimit` header
    keyGenerator: (c) => "<unique_key>", // Method to generate custom identifiers for clients.
    costCalculator: (c) => { return 2; }
  })
);

e.g. based on query params one could decide that the cost for a certain call is more expensive.
this cost should then be used in the counter.

[OllieJennings]

Let me know if this will get added.

Recently started to use this lib, and will eventually need cost calculations per request.

Happy to help out when that time comes as well.

[MathurAditya724]

After thinking about this, I came to the conclusion that it would be far easier to create a new store which supports Cost then to implement in the lib, because of 2 main reasons -

1. Things like the redis store can't work with cost as it uses a script which always increment the value by 1, we can adjust that but then problem 2 comes in
2. Backward compatibility with other stores from express-rate-limit

We won't just need to update the core lib but also all the stores for this, which is a lot of effort. It would be better to create a store based upon your usage, You can learn more about that here - https://honohub.dev/docs/rate-limiter/stores

Happy to assist with its development and list that store in the repo, to help promote it for others.

[psteinroe]

hey, thanks for the work on this lib!

custom stores will not allow a different count for each request. I can understand the importance of compat with express-rate-limit stores though. happy to do a fork but leaving this here as a +1. :)