The company Coinhive used to do this before they shut down. Basically, in order to enter a website, you have to provide the website with a certain number of Monero hashes (usually around 1,024) that the website would send to Coinhive’s miner pool before letting the user through.

It kinda worked, except for the fact that hackers would try to “cryptojack” random websites by hacking them and inserting Coinhive’s miner into their pages. This caused everyone to block Coinhive’s servers. (Also you wouldn’t get very much money out of it - even the cryptojackers who managed to get tens of millions of page views out of hacked websites reported they only made ~$40 from the operation)