Does not work with Cloudflare workers due to dependency on axios

[davidhouweling]

Context

I've been utilising this library for a bot i'm working on and it does work as expected.

However, I'm attempting to convert it to be a Cloudflare Worker and it isn't supported due to some of the capabilities not aligning.

One approach would be to allow for the setup of the authentication to take in a custom axios fetch adapter such as https://github.com/haverstack/axios-fetch-adapter which patches the issue, but ultimately given the support now for native fetch in both browser and Node 18+ it would be worth just switching to native fetch and removing the axios dependency all together.

I've drafted up the work locally and have proven it works at least for the node use case. I'll raise a PR and leave it to project owners if they wish to take it on.