NormalizeHTTPHeaders middleware

[lmammino]

Following several discussions with @vladgolubev and @dkatavic (see #85 and #75) I think we should have a middleware that makes sure that the headers in the lambda-proxy integration from API Gateway are always exposed in canonical format (dash-separated-camelcasing).

The idea of this middleware would be to go over all the available headers and reconstruct the object with all the keys properly normalized.

Thoughts?

[lmammino]

Simple way to normalize header keys:

const assert = require('assert')

const normalize = (str) => str
  .split('-')
  .map((s) => s.charAt(0).toUpperCase() + s.slice(1))
  .join('-')

assert(normalize('content-type') === 'Content-Type')
assert(normalize('x-api-key') === 'X-Api-Key')
assert(normalize('X-Api-Key') === 'X-Api-Key')

[vladholubiev]

@lmammino nice, but beware of some exceptions, see https://github.com/marten-de-vries/header-case-normalizer/blob/master/index.js

[lmammino]

Great finding, thanks @vladgolubev