I used passports.

Everyone agrees that passports aren't made by one company or one country, yet all countries accept passports.

Not everyone can just start making passports though, it's a complicated process of gaining trust and validation as a "real country" before you can issue passports.

One "country" started using a bit of paper that said "trust me bro" and everyone had to treat it as a valid passport. Worse, the way the internet works is that the border guards don't actually see who issued the passport, only that one of the trusted countries produced it.

Having passports this easy to forge means anyone can anyone.