Sites and Files Access Control
Users with files on Google Drive that embed them in a Google Site frequently ask why their files are not visible on their Site.
The sharing settings for files in Drive are separate from the Site sharing settings and need to be set separately - usually to be the same as the Site - they are not 'inherited' from the Site they are shared in.
Fortunately this is easy to do since it is possible to share both Sites and files on Drive - including folders - with Google groups.
Using Google Groups for Access control
Logged in or not logged in
If a user has zero logged-in accounts and visits either a non-existent site or a site that is not public they will be redirected to a login page. If they have at least one logged-in account they are no longer redirected to login
If you want to ensure a user is prompted to sign in to the correct Google account when sent a link to a Google Site then use a link in the form: https://accounts.google.com/AccountChooser/signinchooser?continue=SITEURL
Sites Service disabled for a domain
If users are signed in to an account from a GW domain for which the Sites service has been disabled domain users they will not be able to access ANY Google Site