Fully functioning finished sample code for my Documenting an ASP.NET Core API with Swagger / OpenAPI course.
The code contains everything from basic documentation with OpenAPI / Swagger (using Swashbuckle.AspNetCore) over dealing with not-so-obvious use cases, ApiExplorer, authentication and versioning right up to customizing the UI.
Built with ASP.NET Core 2.2
You can find the course over at Pluralsight: https://app.pluralsight.com/library/courses/aspdotnet-core-api-openapi-swagger/table-of-contents