I'm actually using the remarkable for this kind of functionality. Some article i want to read later --> Share with remarkable, you do need the remarkable cloud service for that work seamless though.
Maybe one could use this to circumvent the paid cloud service.
Author does a good job in separating authentication and enrollment.
Especially that not all authentication factor are equal and the mobile phones are getting it right is on point.
(shameless plug, i'm the CEO, as ubiqu we have build al the tooling necessary to use your phone as a authentication and signing device across all digital channels)
TL/DR: phone as an authentication device is a good idea.
Ubiqu, lets you log in with one app; no username or password, but with the security of a smartcard.
Ubiqu has the same level of security as your bank card, id card, SIM, but now delivered as an app and pin on a mobile phone.
Ubiqu is approx. 10 persons, funded and profitable and growing, selling to banks and telco's and launching free developer product soon.
We are looking for deep developers with a crypto itch or embedded affinity and marketeers that can make their aunt want the impossibly complex for being utterly simple.
Maybe one could use this to circumvent the paid cloud service.