Do you want to allow ArcGIS users to log into your custom web app and access their content? For front-end developers, authentication and authorization can be the stuff of nightmares — luckily, building an app that works with ArcGIS Online and ArcGIS Enterprise is easy! This presentation will introduce OAuth 2.0 and how your custom web apps can leverage it to connect to the ArcGIS ecosystem. Additionally, we will discuss tools like the ArcGIS API for JavaScript and ArcGIS REST JS and how they can streamline the process further.