feat(fetch): support custom credentials in Request

[MichaelDeBoey]

See @kettanaito's remix-run#21

Motivation

I'm adopting this polyfill as a part of a large API change in Mock Service Worker to adhere better to the Fetch API specification (mswjs/interceptors#292, part of mswjs/msw#1404). While doing so, I've spotted that whenever I construct a Request instance, its credentials are always set to same-origin, ignoring any custom credentials value I may supply in request init.

It's absolutely possible and allowed to construct a Request instance with any credentials the consumer needs.

Context: I'm constructing Request instance for an intercepted XMLHttpRequest as a part of the @mswjs/interceptors library. When dealing with XHR, it controls the credentials behavior with its withCredentials?: boolean flag. I must different request credentials values based on that flag to respect the specification and keep the consumer's code consistent.

Changes

• Adds credentials to RequestState
• Updates Request.credentials getter to resolve the value from the internal state.
• Adds missing test suites for request credentials behaviors

CC/ @alanshaw @Gozala

[kettanaito]

👍 Thanks for forwarding this. Let's improve the spec compliance.

[MichaelDeBoey]

@kettanaito Yeah it would be nice to get everything that's in the @remix-run fork back upstream

@alanshaw @Gozala I'm quite certain that if you want to add maintainers to the project, some Remix people (like @jacob-ebey) would be happy to join! 👀

[kettanaito]

@MichaelDeBoey, is there any particular reason Remix still needs these polyfills? Migrating to Next 18 and using the global Fetch API should suit all the needs, should it not?

[MichaelDeBoey]

@kettanaito Fetch API is still marked Experimental in the Node docs, so the team decided to not rely on them (yet) until they're marked Stable