The decision to build or buy an authentication solution, specifically for OAuth, depends on various factors including complexity, required product capabilities, time to market, team constraints, and concerns about staffed project longevity and security risks. Enterprises with simple OAuth requirements, sufficient engineering resources, and a strategic commitment to open source may choose to build their own solution, while those with unique or complex authentication needs, limited expertise, or high security risks are often better off purchasing from a vendor. Vendors like Edge Stack API Gateway offer expertise, scalability, performance, and managed security solutions that can provide a faster time-to-market and lower operational costs compared to building in-house.