
For authentic sources, start with the book The Serpent Power by Arthur Avalon (real name Sir John Woodroffe). He was a Britisher who was a High Court Judge in Colonial India who was so fascinated with the entire subject matter of "Tantra" that he studied Sanskrit under native Indian scholars and translated a lot of Tantric texts into English. For a nice picture book with rare photographs on the same subject matter, see Kundalini: The arousal of inner energy by Ajit Mookherjee.
The above will give you a solid foundation after which you can move on to other original texts.
