Company i work in spent 2 years to implement OAuth. For that time application was rewritten 3-4 times. 3 developers worked on that in different times. And guess

Company i work in spent 2 years to implement OAuth. For that time application was rewritten 3-4 times. 3 developers worked on that in different times. And guess what? It still doesn't work and serves tiny portion of traffic with tons of issues.