This was filed like 6 years ago and I'm not really sure what to make of it. https://dev.archive.openwrt.org/ticket/9138
Just installed the latest patch today on an ER-X-SFP and don't see any package suggestive of providing the desired functionality....
An OpenWRT Noob!
It's not going to be added, not now, nor in 6 years' time - it's fundamentally impossible to do.
Access to the router is most important while it's offline, so anything requiring online services to authenticate is a complete no-go. Keep in mind that 99% of all devices don't have a RTC (and even less a battery powered one), so after rebooting you don't even have a reliable (or just predictable) time base either. Apart from these fundamental issues, the required packages are -in the context of 4, 8 or 16 MB flash devices- are huge and maximal invasive (requiring libpam plugins), they simply aren't usable on most devices running OpenWrt.