Best way to cancel a YARP request

[leastprivilege]

Assume I want to check the existence of certain headers for a specific route - and if not present cancel the request and return a specific error code.

What would be the best extensibility point for that. It would be very similar to a transform provider, but it does not look like this is designed to return errors.

[MihaZupan]

You can specify routing rules based on request headers, see https://microsoft.github.io/reverse-proxy/articles/header-routing.html

"myRoute" : {
  "ClusterId": "myCluster",
  "Match": {
    "Path": "{**catch-all}",
    "Headers": [
      {
        "Name": "X-Custom-Header",
        "Mode": "Exists"
      }
    ]
  }
}

You can then have a different route match the request, or let ASP.NET Core's routing reject the request if it does not match any route.

If you need more flexibility, such as a more complex decision process to determine whether to proxy the request, or sending a custom response, consider using a middleware. See https://microsoft.github.io/reverse-proxy/articles/middleware.html#send-an-immediate-response

[leastprivilege]

Thanks this will work for me.

As a future idea - maybe it would make sense to have request/response validators - similar to request/response transformers.