Asking permission beforehand is a good rule if you can't read body language and non-verbal cues, but not the best choice if you can. It goes without saying, of course, that you respect a verbal "no".

Like, it's not mysterious magical rocket science. Leave a graceful exit path, start small and safe, and gauge their response before escalating. If you're not a dickwaffle, this'll get more positive responses without coming across as creepy or pressuring. If you're not making a game of pushing boundaries or starting with a huge power discrepancy, this process fails really gracefully. Like, really gracefully. Neurotypicals have probably done this dance with you without you or them noticing it.