Anonymous but verifiable/auditable online voting is a very hard problem that does not seem to be solved yet. How do you ensure that the remote voter gets one a

Anonymous but verifiable/auditable online voting is a very hard problem that does not seem to be solved yet. How do you ensure that the remote voter gets one and only one vote while also being able to audit that the intended vote was recorded (it wasn't changed on the wire, in memory or on storage), without linking in any way the vote cast with the voter? Ensuring that remote voting is not done under any form of duress or monitoring seems essentially unsolvable. Incidentally, voting in state elections is compulsory in NSW so your example doesn't fit this case either way.