How to load test OAuth-secured APIs

OAuth is a widely used authentication standard for verifying user identities via third-party services, and it's important for testing both anonymous and authenticated endpoints. The article explores how to load test APIs secured by OAuth using tools like Grafana k6, focusing on authentication methods utilizing Microsoft Azure Active Directory (AAD) and Okta. It delves into OAuth 2.0 authentication flows, highlighting the authorization code flow as the preferred approach and explaining the implicit flow for simplicity and testing. The text also discusses OAuth 2.0 grant types, specifically the client credentials grant for server-to-server authentication and the resource owner password credentials grant for user authentication. The article provides a practical example involving Microsoft AAD, including testing with curl and incorporating OAuth authentication into k6 load test scripts, while offering guidance on implementing and automating these processes.