There is currently no way I know of allowing this functionality that is meaningfully "reliable". At least not without erecting new barriers such as mandatory registration (and verification).
So you, and everyone else, seem to be demanding publishers just switch to "absolute paywalls". You will then have strictly less access than before.
How is that supposed to be better?
But if publisher do want absolute control over who views their content, then they should make people log in. I think that would be a mistake, but it's their mistake to make. I'm just opposed to give them legal control over what I do with my computer and any data their servers freely give me.
Viewed under a magnifying glass, it seems like a good thing to ensure the publishing industry can use soft paywalls, but taking a broader view, I think that breaks the web. I don't think soft paywalls are worth breaking the web, and even more broadly, governments should only regulate what users can do with data willingly sent to their computers in very exceptional circumstances.
It may mean that without a harsh letigious method, publishers do not offer "soft paywalls". It's more likely they will continue to do so to not be shut out of the market, AND we won't have waves of frivolous harsh lawsuits bankrupting independent developers.
The alternative you're proposing is to in effect be held to ransom by content providers - your argument could equally be made for any form of drm or appeasement (without root how do we know you are not recording this, wothout your location how do we know you are within our licensing area, without direct retinal scans how do we know who is really watching, etc)
Compuserve paywalled all of their content way back in the 1980s.
Browsers already have a mechanism for authorizing access to content. Many mechanisms, really. If a company chooses to use an unreliable mechanism, I don't think we are morally obligate to roll over and do what they want.