They say it because as a development exercise it is both seductively attractive and very dangerous. Furthermore, almost no one's authentication problems are uni

They say it because as a development exercise it is both seductively attractive and very dangerous. Furthermore, almost no one's authentication problems are unique or unsolved. There is approximately never a good reason for a team to roll their own authentication solution from the base primitives unless that's both their core competency and their product differentiation. It offers virtually no upside for virtually certain downside.