Implementing systems and processes that allow access to huge amounts of personal information is not easy. Small gaps in implementation or processes can have dire consequences. Imagine an identifcation process gone wrong, and a user receiving someone else's data. Moreover, poor security practices can lead to massive fines.
In cryptography, there is an accepted axiom that "you don't roll your own crypto". Rather than thinking of a poor implementation yourself, we use well-tested and well-designed libraries that do this kind of work for us. We've accepted that using OpenSSL, OAuth and bcrypt provide both qualitative and provably secure benefit to development. This is especially true when compared with systems we can design and implement ourselves. The Open Data Rights API provides a robust set of API design principles that ensure that data is secure and private.