My ex used to do it to me in the shower. It felt great, except after all was said and done. I always had a bit of soap that went it and it sting when I pee the 2 or 3 times after. She used to give me what I call a knob job. But for having my balls and strictly shaft played with, it's enjoyable. I find it highly enjoyable to reverse the roles when I had a FWB who loved to shower together after sex and cuddling. I was the lucky guy - curious enough as well - to discover she could orgasm from her breasts. As I stood behind her in the shower, I considered her breasts needed to be cleaned a lot, a long time. I made her knees go weak and it was so great.
Soap is actually not recommended, as it can remove the natural oils and lubrication, leading to bruised, uncomfortable penis/vagina skin.
Here is a little advice if you must jack off in the shower , find a shower liquid soap made with Shea butter or one for sensitive skin it will help with drying out and prevent burning in most cases. Learned by experience