To create a rewrite rule that will remove the origin port from the HTTP header of incoming requests that are being forwarded to the backend pool, you should configure the following settings:

Common header: X-Forwarded-For
Header value: add_x_forwarded_for_proxy

Explanation:

The "X-Forwarded-For" header is commonly used to identify the original host or IP address of a client when using a proxy, load balancer, or other intermediary device. This header is often used to preserve the client's IP address information when the request is forwarded to the backend.

In this case, you need to remove the origin port from the incoming requests, so you should configure the rewrite rule to use the "add_x_forwarded_for_proxy" option for the "Header value" setting. This will add the client's IP address and port information to the "X-Forwarded-For" header, but without including the origin port.

The other options are not correct:

- "Via" or "X-Forwarded-Host" are not the appropriate "Common header" settings for this use case.
- "client_port" or "host" are not the appropriate "Header value" settings for removing the origin port from the HTTP header....