RuleRewrite()Credentials is what happens to credential headers the sandbox sent, such as Authorization and Cookie: "strip" (the default) removes them, "redact" keeps each with its value replaced by "redacted" (after an auth scheme such as "Bearer "), and "keep" forwards them unchanged.
Host is an HTTPS destination. Exactly one of host and sandbox is set.
Sandbox is the name or ID of a sandbox to send requests to, over plain HTTP.
A sandbox link from this sandbox to that sandbox's port must exist. Exactly one of host and sandbox is set.