Extending an Operation Parent in Minimal API for Power Apps Webhooks

[faramos]

To describe a webhook for Power Apps / Automate, the platform requires an extension in the post operation parent. You can find more details in the documentation.

I have previously implemented this for another product using NSwag and by implementing an IOperationProcessor.

Now, I want to try using OpenAPI.NET, but I'm struggling to extend the generated JSON node for the minimal API group where the operation is added. I have tried implementing IDocumentFilter and using the WithOpenApi() extension method, but both approaches add the extension at the operation level.

Here’s what I have so far:

var casesGroup = group.MapGroup("/when-case-event");
casesGroup.WithOpenApi(o =>
{
    var eventType = typeof(CaseEventWebhookPayload);
    o.Extensions["x-ms-notification-content"] = new OpenApiObject
    {
        { "description", new OpenApiString($"Subscribe to {eventType.Name} event.") },
        {
            "schema", new OpenApiObject
            {
                { "$ref", new OpenApiString($"#/definitions/{eventType.Name}") }
            }
        }
    };
    return o;
});

Is it possible to achieve this in OpenAPI.NET?

Thanks in advance.