Promote query parameters to request headers

Promote a query parameter to a request header by using CEL expressions. The example uses request.uri with the contains() function and a conditional expression to read a query parameter value and inject it as a request header before the request reaches the upstream.

This configuration is useful when a client passes information as a query parameter but the backend service expects it as a header.

Before you begin

1. Set up an agentgateway proxy.
2. Install the httpbin sample app.

Promote a query parameter to a request header

In this example, a client passes a feature flag as the beta query parameter. The backend service expects this as the x-beta-features request header. The transformation reads request.uri and sets the header to enabled when beta=true is present, and disabled when it is absent.

1. Create an AgentgatewayPolicy resource with your transformation rules.

   kubectl apply -f- <<EOF
   apiVersion: agentgateway.dev/v1alpha1
   kind: AgentgatewayPolicy
   metadata:
     name: transformation
     namespace: httpbin
   spec:
     targetRefs:
     - group: gateway.networking.k8s.io
       kind: HTTPRoute
       name: httpbin
     traffic:
       transformation:
         request:
           set:
           - name: x-beta-features
             value: 'request.uri.contains("beta=true") ? "enabled" : "disabled"'
   EOF

2. Send a request with the beta=true query parameter. Verify that you get back a 200 HTTP response code and that the x-beta-features header is set to enabled in the headers echoed back by httpbin.

   Cloud Provider LoadBalancerPort-forward for local testing

   curl -vi "http://$INGRESS_GW_ADDRESS:80/get?beta=true" \
    -H "host: www.example.com:80"

   curl -vi "localhost:8080/get?beta=true" \
   -H "host: www.example.com"

   Example output:

   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   ...
   
   {
     "args": {
       "beta": [
         "true"
       ]
     },
     "headers": {
       "Accept": [
         "*/*"
       ],
       "Host": [
         "www.example.com"
       ],
       "User-Agent": [
         "curl/8.7.1"
       ],
       "X-Beta-Features": [
         "enabled"
       ]
     },
     "origin": "10.244.0.6:12345",
     "url": "http://www.example.com/get?beta=true"
   }
   

3. Send a request without the beta=true query parameter. Verify that the x-beta-features header is set to disabled.

   Cloud Provider LoadBalancerPort-forward for local testing

   curl -vi http://$INGRESS_GW_ADDRESS:80/get \
    -H "host: www.example.com:80"

   curl -vi localhost:8080/get \
   -H "host: www.example.com"

   Example output:

   < HTTP/1.1 200 OK
   HTTP/1.1 200 OK
   ...
   
   {
     "args": {},
     "headers": {
       "Accept": [
         "*/*"
       ],
       "Host": [
         "www.example.com"
       ],
       "User-Agent": [
         "curl/8.7.1"
       ],
       "X-Beta-Features": [
         "disabled"
       ]
     },
     "origin": "10.244.0.6:12345",
     "url": "http://www.example.com/get"
   }
   

Cleanup

kubectl delete AgentgatewayPolicy transformation -n httpbin