An official nation-state institution, like the Swedish Skatteverk, could easily let their citizens verify themselves online. O-auth tokens could be created by the nation-state institution, generated server-side, and these tokens could be used to verify legal identity within the app-space.
What kind of APIs do nation-states have for this?
Example market: there's a host of services that right now scan people's passports, coinbase.com, snapswap.us, and these could instead use o-auth tokens generated server-side.