Reshape a flow without touching the service.

# Enriching a flow without touching the upstream: named policies, a CEL condition, composed
# global -> host -> routes -> operation, the most precise wins, `!name` removes.
version: 1
contracts:
  openapi: ./openapi.yaml
upstreams:
  default:
    url: http://orders.internal:8080
auth:
  issuers:
    - name: customers
      discovery: https://login.example.net/.well-known/openid-configuration
      audience: api
policies:
  definitions:
    plan-header:
      type: header-inject
      when: "has(auth.subject)"                   # CEL: authenticated callers only
      config:
        set: { x-plan: "{{ auth.claims.plan }}", x-operation: "{{ route.operation_id }}" }
        on_missing: skip                          # skip | empty | fail - required for an expression
    strip-server:
      type: header-remove
      phase: response                             # on what the upstream answers
      config: { names: [server, x-powered-by] }
    v2-path:
      type: rewrite-path                          # the upstream's path, never the served one
      config: { to: "/v2/orders/{id}" }
    channel:
      type: query-inject
      config: { set: { channel: gateway } }
  chains:
    global: [strip-server]
    routes:
      "/orders/*": [v2-path, channel]             # * one segment, ** any number