Article: https://medium.com/@leondo/unity-engine-metamask-wallet-6797d4699e45
Automagically connect your Unity game to Metamask
Create a folder called WebGLTemplates
under /Assets
Download Web3Template
from here and paste under WebGLTemplates
In Unity
Change template
Build as webgl
// Web3Template/TemplateData/web3Connect.js
if (window.ethereum) {
web3 = new Web3(window.ethereum);
// connect popup
ethereum.enable();
} else {
alert("Non-Ethereum browser detected. Please connect to a wallet");
}