SDK Authentication Handling Improvements (Suggestions?)

[domwebber]

This issue stands to discuss possible improvements to the way that this SDK handles authentication. Any suggestions are appreciated!

Ideally, authentication needs to be able to be overridden at an API call level as a number of APIs require different auth methods - App Access Tokens, System User Access Tokens, Business Integration Access Tokens.

Currently, authenticating with the SDK requires adding the following code to either the SDK's instantiation or each call for usage:

const sdk = new Client({
  // The following:
  request: {
    headers: { Authorization: "Bearer ..." },
  },
});