Hi, Viwe.
I've been working with my young nieces who are still trying to get a good grasp of English. Although "may" and "can" both are words that ask for permission. We never use "may" when referring to someone else's permission to do something. We do, sometimes say, "[...] If you may" but it is a bit of an archaic phrase that still plays to the rules of may being possessed by the target of the sentence.
TL:DR: May is only used when referring to the ability/permission to do something.