@sentry/browser - Support fetchOptions

[dcherman]

In the original raven-js client for Sentry, it was possible to customize the options sent to fetch; it doesn't look like the transport in @sentry/browser supports that today.

sentry-javascript/packages/browser/src/transports/fetch.ts

Lines 14 to 27 in 2f46059

	const defaultOptions: RequestInit = {
	body: JSON.stringify(event),
	method: 'POST',
	// Despite all stars in the sky saying that Edge supports old draft syntax, aka 'never', 'always', 'origin' and 'default
	// https://caniuse.com/#feat=referrer-policy
	// It doesn't. And it throw exception instead of ignoring this parameter...
	// REF: https://github.com/getsentry/raven-js/issues/1233
	referrerPolicy: (supportsReferrerPolicy() ? 'origin' : '') as ReferrerPolicy,
	};
	return this._buffer.add(
	global.fetch(this.url, defaultOptions).then(response => ({
	status: Status.fromHttpCode(response.status),
	})),

My use case is that our instance of Sentry lives behind an endpoint that uses cookie auth, however it's on a separate subdomain from the applications generating the errors. As a result, we need to use credentials: 'include' on fetch in order to pass cookies along.

[pmjhonwang]

same problem,
real need credentials: 'include' options

[kuangp]

I also have the same use-case. Can we expose this feature in the new SDK as part of TransportOptions (https://github.com/getsentry/sentry-javascript/blob/master/packages/types/src/transport.ts#L26)?