In 2012, GitHub faced challenges in expanding due to its outdated authorization system, prompting the need for a refactor led by Rick Bradley. The key challenge was not only building a new system but understanding the existing one, which resulted in the development of Scientist, a Ruby library that safely refactors critical code paths through controlled experiments. This tool allowed GitHub to compare old and new code behavior in production without risking system failures. The complexity of authorization migrations stems from the deeply intertwined nature of authorization logic within applications, especially in microservice architectures, leading to challenges in understanding and changing legacy systems. To address these challenges, Oso introduced Oso Migrate, a tool designed to streamline the migration process by providing utilities and APIs that enhance the speed and safety of transitioning to new authorization systems. Oso Migrate includes features like a policy debugger and a Parity API, which offer insights into authorization decisions and help maintain consistency during migration. These tools help teams manage complex authorization logic by facilitating a test-driven, incremental migration strategy, ensuring that both old and new systems operate in tandem until parity is achieved, thereby easing the transition to Oso Cloud.