Respect "X-Forwarded-Proto" header from Cloud Flare / other frontends
Cloud Flare correctly sets the "X-Forwarded-Proto" to "https" when using their "flexible" option (https://support.cloudflare.com/hc/en-us/articles/200170986-How-does-Cloudflare-handle-HTTP-Request-headers-) - this is the same as if we used the GCP load balancer directly to handle HTTPS and proxy via HTTP to our backends.
I need my backend services, which listen on HTTP, to understand that the request came from a client using HTTPS - but Google Cloud load balancer is overwriting the X-Forward-Proto header to "http", even though the client is actually using HTTPS from our Cloud Flare frontend.
This is the whole point of the "X-Forwarded-Proto" header, so I'm not sure why the load balancer decides to ignore it and reset it to an incorrect value.
Please provide a way for us to deal with this correctly. Even if we need to somehow set trusted frontends or whatnot.