[aaronax]

Actually issued by a government? Not sure.

How to implement? Also not sure. I am not an expert in this field. "Anonymous credentials" seems like the closest thing maybe. Basically you need to somehow prove you have a valid signed certificate without disclosing the public key.

https://crypto.stackexchange.com/questions/83412/how-to-achi... https://crypto.stackexchange.com/questions/52189/zero-knowle...

Since you seem open to putting up barriers...in the process of looking into this I discovered Idena and checked it out a little. You could required verified Idena something or other, just as an example. I'm sure there are scores of these types of things being built, most or all of which will fail to gain traction.