closes https://github.com/TryGhost/Team/issues/1161
- when a site is in private mode, design previews, the portal previews on membership, customize portal and offer pages were unable to load.
- For design and theme previews, the request to fetch preview data was failing due to cors and cookie not attached when admin and frontend have split urls.
- For portal and offer previews, there was no authentication done on private site before load, so if user opened the pages directly on them it failed to load the site.
- this change adds a new service that authenticates private site from admin as soon as user session is loaded, so previews on settings will always find the authenticated session for private sites and load correctly.
- it also updates fetch method for previews to include credentials so they are always able to fetch the site data after login
- removes authentication from site route since that was done as its now centrally taken care of by the frontend service
65495b528f