Allow passing URLSearchParams directly to implicitAuthentication

[nwalters512]

Given that the function is already using URLSearchParams internally, it seems like a natural extension to allow one to pass an instance of URLSearchParams if they already have it. This makes implicitAuthentication usable even when one doesn't have a web Request object.

[nwalters512]

I couldn't figure out how to get these tests to run locally. Even when running npm run tap:node locally, every test fails with the following:

  message: "Promise rejected during \"end-to-end w/ response_type=id_token, implicit, form_post, error_response\": unexpected HTTP response status code"

Any guidance would be helpful!

[panva]

Hello @nwalters512

I'm not sure in what case the existing inputs aren't "usable". The examples cover the use cases I have in mind.

[nwalters512]

"When using a form_post response mode without a Request instance" from those docs matches my scenario. While that works, it's simply very clunky to require one to construct a full URL. It seems especially silly given that implicitAuthentication will immediately unpack things back into a URLSearchParams instance. If I already have a URLSearchParams, it seems like I should just be able to pass it directly.

I should have said this PR makes it more usable (or rather, more ergonomic).