Worked on the mattermost/mattermost repository to enhance the security and reliability of guest onboarding by addressing a race condition in the guest magic link authentication flow. Implemented atomic token consumption using Go, ensuring that guest magic link tokens are single-use and cannot be reused, which aligns with existing SSO token handling patterns. Focused on backend and API development, the solution applied the ConsumeOnce pattern to prevent token replay attacks and improve authentication robustness. Emphasized thorough testing to validate the new token handling logic, resulting in a more secure guest authentication process without introducing new features during the development period.