An Illustrated Guide to OAuth

OAuth secures third-party app access to user data without sharing passwords. For services like YNAB connecting to Chase Bank, users log in directly with the data provider, authorize specific permissions, and return to the original app with an authorization code. The app exchanges this code for an access token via a secure back-channel request. This process protects credentials, limits access scope, and prevents token interception, allowing apps to safely act on a user's behalf while maintaining user control over their data.