Cannot customise the HTTP provider in v6?

[davidgiven]

Is your feature request related to a problem? Please describe the problem.

The v5 SDK had a builder interface to GraphServiceClient which allowed specifying an IHttpProvider which was used for all HTTP requests; this was great if you were using a customised HTTP interface. However, the builder interface appears to be missing in v6, and instead you have to pass in an OkHttpClient, which cannot be customised in the same way.

Describe the solution you'd like.

Can we have an IHttpProvider interface like in v5, please? (Or else point me at equivalent functionality I haven't found yet!)

Additional context?

No response