the participants will be volunteers from the public
Given that, I don’t see any way to achieve your goal, at least on iOS.
iOS has a general policy that highly intrusive network monitoring [1] can only be deployed to supervised devices [2]. If these users are using their own devices then they can’t be supervised.
Folks often try to get around this privacy policy by abusing the packet tunnel provider mechanism. This generally doesn’t end well, which is why we published TN3120 Expected use cases for Network Extension packet tunnel providers.
Moreover, even if you manage to get yourself into a privileged network position where you can see all traffic, that doesn’t let you “track and intercept network requests from a device”. Apple is in the process of rolling out more and more on-the-wire privacy features — things like iCloud Private Relay — that are specifically designed to prevent someone in a privileged network position from being able to see what the user is doing.
All of the above is from a networking perspective. There may be other options in the Safari extensions space. I’m not an expert on that technology, so I can’t offer any answers there. If you want to explore that, I recommend that you start a new thread with appropriate tags (Safari, Safari Extensions, and so on).
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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"
[1] This includes NE content filters but also things like the global HTTP proxy payload in a configuration profile.
[2] There are some exceptions to this for content filters. For the details, see TN3134 Network Extension provider deployment. However, I don’t think any of those exceptions will help you.