You can get a digital certificate, such as the idCAT (the FNMT also issues them). I have mine loaded into a smart card because that's just how I roll, but eithe

You can get a digital certificate, such as the idCAT (the FNMT also issues them). I have mine loaded into a smart card because that's just how I roll, but either way it's equivalent to the DNIe; you can use it to authenticate to all the government agencies.