[THREESCALE-2775] [Policy] IP Check uses multiple x-forwarder-for headers.

[eloycoto]

This change allows to block traffic when multiple x-forwarder-for are defined
in the same request. Resty creates an array with all duplicated headers, so in
case of a array only the first heaeder will be used.

Also, adds the integration test to make sure that no regression in this case.

Example request to make it fail:

curl localhost:8080?user_key=123
    -H "X-Forwarded-For: 1.2.3.4" \
    -H "Host:one" \
    -H "X-Forwarded-For: 1.2.3.44"  \
    -v

config:

{
  "services": [
    {
      "id": 200,
      "endpoint": "http://localhost:8080",
      "backend_version": "1",
      "proxy": {
        "service_backend_version": "1",
        "hosts": [
                  "one"
              ],
        "api_backend": "https://echo-api.3scale.net:443",
        "proxy_rules": [
          { "pattern": "/", "http_method": "GET", "metric_system_name": "hits", "delta": 1 }
        ],
        "policy_chain": [
          { "name": "apicast.policy.apicast" },
          {
            "name": "ip_check",
            "version": "builtin",
            "configuration": {
              "error_msg": "IP address not allowed",
              "client_ip_sources": [
                "X-Forwarded-For"
              ],
              "ips": [
                "1.2.3.4"
              ],
              "check_type": "blacklist"
            }
          }
        ]
      }
    }
  ]
}

Fixes #1061

Signed-off-by: Eloy Coto eloy.coto@gmail.com

[davidor]

Should be X-Forwarded-For instead of Host.

[davidor]

Added a minor comment.

Looks good 👍