Unfortunately 'authentic' is a fairly broad term. India is a big place and they do things differently from one region to another.
Madhur Jaffrey is certainly good - I have read most of her books at one time in the past (I have been cooking Indian food for about 30 years) and there are other good authors. I have found the best thing to do is to read a few different ideas on the same dish and try to figure out what is common and particularly look for the regional origin of the dish.
I am just starting a website of my own on Indian food (all my own recipes, tried and tested) have a lookMy Indian Food