But, you (because you are so sure about the best method) by sure know, that the laws are explicitly for non-physical goods, where no delivery-address must be provided, right?
Here is a link, how one company is doing it (forget about government information, they seldom go so much in details!): https://rachelandrew.co.uk/archives/2014/12/08/consensus-and...
They use the IP address to validate the user given address and for later proof.
BTW: Downvoting all the time does not help the discussion. I try to discuss this topic seriously and I was bringing some very relevant topic here, and am constantly downvoted. (It is not my fault, that the EU came up with such laws, and provide no useful guide how to implement it!)