sveltekit needs to actually set the cookie headers etc. if credentials is true
Broken link. Correct permalink: https://github.com/sveltejs/kit/blob/a59fbd07caa3fbee22b8c4abbf065be623c774d4/packages/kit/src/runtime/server/page.js#L133
In more recent version, it does set the cookie header: https://github.com/sveltejs/kit/blob/5f7fdbcfdc2ce02d613aa287778a50b064a872db/packages/kit/src/runtime/server/page/index.js#L122