Webrecorder's WACZ signing spec (https://specs.webrecorder.net/wacz-auth/latest) does some of this — authenticating the identity of who archived it and at what time — but the rest of what you're asking for (legitimacy of the content itself) is an unsolved problem as web content isn't all signed by its issuing server.
In some of the case studies Starling (https://www.starlinglab.org/) has published, they've published timestamps of authenticated WACZs to blockchains to prove that they were around at a specific time... More _layers_ of data integrity but not 100% trustless.
In some of the case studies Starling (https://www.starlinglab.org/) has published, they've published timestamps of authenticated WACZs to blockchains to prove that they were around at a specific time... More _layers_ of data integrity but not 100% trustless.