AB-400 Explained: Building Power Platform Custom Connectors with OpenAPI, Policies, and Code

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Learn how to build Power Platform custom connectors with OpenAPI, policy templates, and custom C# code in this AB-400 Explained session. Explore how to define stable API contracts, configure authentication, adapt requests, and transform backend responses for Power Apps and Power Automate. Keep connector adaptations separate from backend authorization and business logic. Topics covered: • Custom connector architecture and the API invocation path • OpenAPI 2.0 definitions, stable operation IDs, and x-ms-summary annotations • API Key authentication for Azure Functions • OAuth 2.0 with Microsoft Entra ID and connector Redirect URIs • Connection creation and credential handling • Policy templates for constant query parameters and request adjustments • Custom C# transformations with ScriptBase and ExecuteAsync() • Flattening nested JSON responses and detecting backend contract mismatches • Testing success, authentication, validation, outage, and malformed-response scenarios • Versioning connector definitions, policies, and scripts together for repeatable ALM deployment For learners preparing for AB-400 and developers connecting Power Apps and Power Automate to external APIs. #AB400 #PowerPlatform #CustomConnectors