Extract api package

This is the first step towards genericizing the google_auth_proxy to support
OAuth2 providers other than Google as discussed in #65. The `api` package will
enable multiple providers to use the same `api.Request()` implementation.

api/api.go

@@ -0,0 +1,32 @@
+package api
+
+import (
+	"errors"
+	"io/ioutil"
+	"log"
+	"net/http"
+
+	"github.com/bitly/go-simplejson"
+)
+
+func Request(req *http.Request) (*simplejson.Json, error) {
+	httpclient := &http.Client{}
+	resp, err := httpclient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	body, err := ioutil.ReadAll(resp.Body)
+	resp.Body.Close()
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode != 200 {
+		log.Printf("got response code %d - %s", resp.StatusCode, body)
+		return nil, errors.New("api request returned non 200 status code")
+	}
+	data, err := simplejson.NewJson(body)
+	if err != nil {
+		return nil, err
+	}
+	return data, nil
+}