Does anyone know how to create a custom stroke in Indesign? I want it to be stars.

InDesign don't have such a feature and as guys says here - you can use it Illustrator for it and do place .ai. 

Therefore - https://indesign.uservoice.com/forums/601021-adobe-indesign-feature-requests/suggestions/20610502-custom-stroke-styles - add your voice here it can help for the future releases. 

There are several special strokes, which can be added. E.g. Woof, Feet, Lights, Rainbow (parallel lines) and some others. Only adding a new stroke will add such funny lines. But stars is not available.

The best way is to create it in Illustrator (don't do it in Photoshop!) and import it as AI file. Photoshiop would decrease Quality, rasterize and increase file size).

I knew I had it somewhere! You can't actually add a "stars" stroke style, but the hack I remembered was posted by David Blatner, not by Barb Binder. You can use the Type on Path tool to fake up a custom dashed stroke.

I think you can, actually. I've never done it before myself, but this article seems to offer step-by-step instructions. 

I had that one saved in my bookmarks as "custom stroke styles" from years ago, but actually now that I have read it more carefully, it looks like it's not actually possible to pull it off. I'm going to keep digging, though, as I am sure that this is not the first time I've looked into this question.

I guess you'd have to create the brush and draw whatever you want to draw in Photoshop, and then import (with transparent background) into InDesign.

You can't.