function generateKey() {
	let result = '';
	for(let i=0; i<16; i++) {
		let idx = Math.floor(Math.random() * CHARS.length);
		result += CHARS[idx];
	}
	return result;
}
Generate a key for use with the local developer API. This does not generate
a secure key, but the Mi Home app does not seem to do that either.