Let's say that I want to build an online service which requires people to be from where they claim to be and restricts multiple accounts.

In Portugal there is an official government authentication portal which can be used just like "Login with Google/Facebook" account is. That way I can require people to give their citizen Id's in order to join my service, but I don't want to restrict it to my country, I want it to work in Europe.

Are there identical services for other countries?

Is there any EU-wide equivalent which at least lets me know the country of the user? (Same question for non-EU countries)

Any alternative? What would you do to know that a user is a real person (not a fake identity), assure that his/her location is real? (Knowing the country is good enough) Manual validation is not an option.

PS: Talking about some open source non profit service, so going through bureaucracy and having to deal with secrets are not options.