Integrate ITransformProvider with ITransformBuilder.Create Method

[PascalSenn]

Hi there,

I'm currently using YARP to forward requests directly with MapForwarder, as well as through Duende BFF, which uses YARP internally.

I'm implementing a token exchange mechanism and need to intercept the request headers. I believe using the ITransformProvider would be suitable for this task, as it allows appending RequestTransform to the route.

However, I've encountered a problem: both MapForwarder and Duende BFF call the Create method, which does not execute any of the transform providers, as seen in the following code snippet:
TransformBuilder.cs - Lines 139-179.

Currently, it appears that there's no way to apply a generic configuration across all YARP use cases. Overriding ITransformBuilder seems the only way, but the default implementation is internal which doesnt make this easier.

I think adding the ITransformProvider capabilities to the Create method would pretty much solve all of these issues.

What are your thoughts on this approach? Is there anything I might have overlooked?

Thank you!