What is the Best wash or glaze for bread when trying to achieve a crunchy crust on Rolls
You may have to compromise a bit here, I am assuming you want both a shiny and crunchy finish to your rolls.

Traditionally, the crunch comes from a longer period in the heating oven with lid removed from the Dutch oven to crisp-up the outer layer. A different technique is used with baguettes, where they are sprayed with fine mist at 5 minute intervals over a total cooking time of 15 minutes. Both of these methods will give an excellent crunch, although the final finish will be dull.

An egg or milk wash will give a lovely final sheen to your rolls, but in my experience this prevents the development of a really crispy crust if you use a whole beaten egg. Apparently, just using the egg white diluted with water will achieve more crunch, but I doubt if it will be as intense as the traditional DO or spray method. 

https://www.thespruceeats.com/egg-wash-yeast-breads-rolls-3057783