##Requirement for HMAC secret key
- http://www.codeproject.com/Articles/704865/Salted-Password-Hashing-Doing-it-Right
- https://paragonie.com/blog/2016/02/how-safely-store-password-in-2016
- http://security.stackexchange.com/questions/4789/most-secure-password-hash-algorithms
- https://hynek.me/articles/storing-passwords/