Display and test openapi.yaml file

From a partner company I got a `openapi.yaml` file to evaluate their api for our use cases. Mostly I know those files from working with ASP.NET Core Apis + Swagger UI, but this time it was just a standalone file. I got the file and an api key for the sandbox. ## Did not work: Use via ASP.NET Core swagger The first thing I was trying was to use the already known swagger ui as it's the same format. So: 1. Setting up a new ASP.NET Core Api project in Visual Studio 2. Including the latest `Swashbuckle.AspNetCore` nuget 3. Putting the `openapi.yaml` file in the `wwwroot` folder 4. Setting up the Program.cs ```cs var builder = WebApplication.CreateBuilder(args); var app = builder.Build(); app.UseHttpsRedirection(); // Allow to serve the unknown-by-default file type .yaml var provider = new FileExtensionContentTypeProvider(); provider.Mappings[".yaml"] = "application/yaml"; app.UseStaticFiles(new StaticFileOptions { ContentTypeProvider = provider, }); app.UseSwaggerUI(c => { c.SwaggerEndpoint("/openapi.yaml", "Imported API"); c.RoutePrefix = "swagger"; }); app.Run(); ``` 5. Accessing the api via https://localhost:7298/swagger This worked almost, but then CORS came around :-( > Access to fetch at 'https://sandbox.***.com/api/...' from origin 'https://localhost:7298' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. The problem seems to be the browser, so let's look for a non-browser-solution. ## Did work: Import in Postman Then I noticed that Postman got the functionality to import openapi spec files:  From here it's possible to simulate the api requests just as good (or better?) as in swagger UI.