Improve HTTP Client Implementation

[hiranya911]

We need to improve and refactor our HTTP client code. Currently we are using a SignedApiRequestHandler abstraction that uses the https package under the hood. This implementation is quite complex to understand and extend. It is also not very amenable to testing. I propose we explore alternatives, and come up with a simpler, more readable and more testable abstraction for making HTTP calls.

Admin SDK relies on many remote REST APIs and we need a solid HTTP client layer that is both robust and easy to use.

[google-oss-bot]

Hey there! I couldn't figure out what this issue is about, so I've labeled it for a human to triage. Hang tight.

[google-oss-bot]

Hmmm this issue does not seem to follow the issue template. Make sure you provide all the required information.

[NeoLegends]

We've just had the need to do a batch processing on all of our existing users (ie we need to do heaps and heaps of requests), and I noticed that there is some room left for performance implementation within the current HTTP stack. For example, you're not using an https.Agent to cache DNS lookups and Keep-Alive-Connections, which seems to hurt performance quite a bit.

[hiranya911]

@NeoLegends can you put a pull request together?

[hiranya911]

This has been implemented. Auth module is already using it, and others will be migrated soon.

[hiranya911]

This has been rolled out to all the modules that make HTTP calls.