[Docs] Extendable Middleware

[austencollins]

Many API Gateway implementations have extendable middleware (e.g., Kong Plug-ins). How could we add this to the current implementation?

Example Use-Cases:

• Custom authorization
• Subscription filtering rules
• Event enrichment
• Custom validation

[mthenw]

IMHO for mentioned use cases, we need two different things: plugins & middlewares.

Plugins

Plugins: something that extends the gateway on a low-level, giving access to internal structures, and many integration points. It's a low-level access that's why it's fast and might be used without heavily influencing overall perf (Tyler will kill me for that statement :D). Implementation options:

• native golang plugins - incoming feature allowing loading .so files with functions and variables exported - downside is that it requires golang knowledge
• RPC on local network - Hashicorp approach go-plugin
• Lua scripting built-in - Redis, nginx approach allowing running lua scripts. This is how Kong plugins are implemented and I'm not sure if Kong, in general, is not written in Lua.

Middleware

Serverless function that runs before some other function and has the ability to change parameters/context or result. Simple to implement: during function registration, a user can specify pre/post middleware/hook. A middleware/hook is a function from the discovery:

Example register function payload:

{
  "functionId": "grapqh",
  "awsLambda": {
    ...
  },
  "middlewares": {
    "pre": "auth"
  }
}

Maybe "hooks" is not the best name, maybe middleware