User scripts are small programs, usually written in JavaScript, to modify and enhance websites. They run within the user's browser and Therefore need no permission of the website operator.
install a user script manager (I personallt use Violentmonkey)
install my scripts
The Jira User Script was discontinued and replaced by:
https://chrome.google.com/webstore/detail/jira-quality-of-life-exte/folmfdcdedbbppdmdjmahilddgdggego