Support to custom quota project

[ruyadorno]

Feature Description

Add param to allow an user to define a custom quota project when connecting to CloudSQL Admin APIs.

[edosrecki]

@ruyadorno this is already supported, by using GOOGLE_CLOUD_QUOTA_PROJECT env var:

https://github.com/googleapis/google-auth-library-nodejs/blob/5f296c37390ba71aa3aa1e4259ff7c525eeaad7c/src/auth/googleauth.ts#L339

[enocom]

Nice find! We should document that here, but also add an explicit API option too to match the other Connectors.

[edosrecki]

If I did not miss something, there is currently no other way to pass quotaProjectId to google-auth-library. It either reads it from the credentials JSON, or overrides it from the GOOGLE_CLOUD_QUOTA_PROJECT env var.

[ruyadorno]

@edosrecki you're right it doesn't look like there's a programmatic API support to it other than the environment variable.

I believe that there's a case to be made to contributing a new API to google-auth-library to add that support.

[enocom]

In that case, we might let this sit for now. I'd suggest folks upvote the original comment if they want this and we'll prioritize accordingly.

[ruyadorno]

Caught up with @danielbankhead last week that showed me googleapis/google-auth-library-nodejs#1663 which normalized a quotaProjectId option for all auth clients. I believe that with that shipped in google-auth-library@9.2.0 we should be unblocked now to add programmatic API support to it.

[ruyadorno]

Given that #238 enabled using any custom auth to be set I believe that a reliable way to support this is to document setting the value via auth property, e.g:

import {GoogleAuth} from 'google-auth-library';
import {Connector} from '@google-cloud/cloud-sql-connector';

const connector = new Connector({
  auth: new GoogleAuth({
    quotaProjectId: "<custom quota project>",
  }),
});

Any thoughts @danielbankhead ?