Yes it is possible but there are some requirements that need to be met by the exterbal site.
The setup and requirements are discussed here:
https://docs.q2developer.com/guides/frontend_development/enhanced_sso.html
"additionalDomains" does need to be added to your config. Not sure I understand what you mean by "still see the original front end widget"... But around "does not require authentication first" would be more of a function about your authentication mechanism (SAML, OIDC, HMAC, etc). If you want to get together and discuss some specifics, go ahead and open up a ticket and we can get on a call.
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