getRandString function
Generates a random string to be used as the VisibilityDetector
key.
Technically this limits the number of editors to a finite number, but
nobody will be embedding enough editors to reach the theoretical limit
(yes, this is a challenge ;-) )
Implementation
String getRandString(int len) {
var random = Random.secure();
var values = List<int>.generate(len, (i) => random.nextInt(255));
return base64UrlEncode(values);
}