Change hashing function 

Is it possible to change the hashing function (MD5) to something else? Like SHA-256 or SHA-512? It seems like right now every hash function uses MD5 and there's no way to change that either through config or custom extension. Would be ideal if it were possible to specify as a config parameter. Or what I would like to do is use a hashing function that is HMAC compliant in place of hashptid. 