Update: The issue appears to have been resolved after upgrading to iOS 11.3. It was observed in iOS 11.2.
When browsing the Web on my iPhone X with Safari, when ever I go to one particular site I occasionally see what appears to be a Face ID validation scan being reported. For e.g., when I land on the website, I see the Face ID overlay superimposed with a spinning and rotating circle, and after a short time the Face ID happy face icon (the one which appears upon successful validation). It disappears a few moments later.
I have occasionally observed this on Slashdot website. It appears every time Safari is relaunched and the aforementioned site is opened. I have not seen this happening on any of the other websites that I browse on my iPhone. However, as I only regularly browse a handful of websites on my iPhone, there may be some reporting bias here.
I don't think this is an HTTPS issue as all the major websites that I visit run over HTTPS.
So, what is special about Slashdot and Face ID? Or is it something set up by Slashdot?
Best Answer
Face ID should only ask for verification in Safari when using Autofill to fill in a username/password. I attempted to duplicate your issue myself with both Safari and Google Chrome, but received no such prompt for verification. Do you have an account on this website? If so, perhaps there is a login box somewhere on the website's home page that Autofill is attempting to fill. If not, it may be a bug with the website, Safari, or your OS. If it is a website bug, requesting the desktop version of the website and seeing if you are still promoted for Face ID could be a good test of that.
If all else fails and it annoys you too much, contact Apple.