It's not going to be added, not now, nor in 6 years' time - it's fundamentally impossible to do.
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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.