While remaining within the "Hinduism is some type of religion" idea, Koenraad Elst describes the nature of religious authority in Hinduism, in this transcript of a talk that he gave in 2009, on the theme "The Founder of My Religion".
In Hinduism, authority rests with a vast array of scriptures: the Veda-s and the Bhagavad-Gita most famously, but also in the Agama-s or doctrinal scriptures of all the various sects, such as the Nanak Panth (= Sikhism)'s Guru Granth. But more importantly, it rests with every enlightened master, everyone who visibly embodies the sacred. It rests with your parents and personal teachers, and ultimately also with yourself. Your own common sense and intuition are the most important guide in your life's choices, informed by the plethora of Hindu sources of light, and not excluding even the non-Hindu sources. Living Hinduism is an application to the religious sphere of "the wisdom of crowds", the principle the combined insights of many provide a more accurate guide than the insights of an individual, be he prophet or messiah. I note with satisfaction that the Ahmadiya movement has incorporated a bit of this Hindu attitude by acknowledging Krishna and the Buddha as legitimate religious teachers.
May all beings in the Universe be happy.