Safari and other WebKit-based browsers automatically probe for
apple-touch-icon.png, apple-touch-icon-precomposed.png, and sized
variants (e.g. apple-touch-icon-152x152.png) at the domain root as
soon as a page loads, even without a matching <link> tag. This is a
background fetch unrelated to what the user actually navigated to, so
it should never become the URL a user is redirected to after
authenticating, just like the existing favicon.* exclusion.
This also refactors the single-pattern favicon matcher into a small
list of ignored background-request patterns so more patterns can be
added going forward.
Closes gh-19692
Robert Winch
242a779034