You Don’t Need Permission
What is now called "agile" (which has been bastardized from the late 90's "XP") is specifically designed to stop this from happening: every day, you have to "stand up" and recite what you did yesterday and what you're going to do today.  If "scrum" is being followed properly, there's somebody listening who's actually recording what you said you were going to do yesterday and compare it to what you say you did yesterday and call out any discrepancies.  So no, you don't need permission to do something as long as it only takes an hour or so and you can hide it somewhere in your daily standup tasks.  Anything that takes longer than this needs to be reviewed and approved - and this is entirely the point of the methodology and the only reason it's ever adopted.