perf: Improve performance by caching verifier

[SeanReece]

Description

Closes: #358

This PR fixes an issue causing fast-jwt verifier to be recreated on every request, which means the fast-jwt cache was not being used. By caching the fast-jwt verifier based on the options passed in, an existing verifier instance can be reused to verify incoming request JWTs instead of having to recreate a new verifier, and then the fast-jwt cache can be utilized (if enabled).

Benchmarks

Tested using a simple fastify server with autocannon used to create load

No auth: 77,978 req/s

Changes (no cache): 53,008 req/s
Changes (cache): 60,880 req/s

Main (no cache): 46,302 req/s
Main (cache): 34,669.1 req/s

Very odd behaviour on current main where enabling cache has a performance impact, I believe this is caused by fast-jwt having to recreate cache on every request.

Config used:

fastify.register(require('@fastify/jwt'), {
  secret: 'supersecret',
  decode: { complete: true },
  verify: {
     cache: true, // disabled for "no cache" tests
  },
})

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[kibertoad]

@SeanReece ping! do you need any help with this?

[SeanReece]

@kibertoad Thanks for reaching out - work has just been busy lately. I've been spending a bit more time getting familiar with the fastify-jwt source and I think I have a better solution instead of caching verifier instances. Hoping to have something today.

[SeanReece]

a new decoder was also being created on every request (see line 478), this ensures we will use the global decoder if the default/global settings are used.

[SeanReece]

Just moving this from below to preserve options passed in even when using promises.

[mcollina]

lgtm

[kibertoad]

great job!