What are the authentic traditional ingredients for Naan bread?
Naan traditionally is plain flat bread made using bread flour, Yeast, salt and water. Its cooked in tandoor.

Salt could be optional if you are having naan with a curry. (Cause curry usually has salt and the bread might not need it).

Variations like milk or yogurt is used instead of water to make dough soft and fluffy. This would change the texture and flavor of the bread.

It is possible to use baking powder instead of yeast, because they both act as a leavening agent. Don't use them together. 

IMHO eggs are not part of the traditional naan ingredients.