proxy: use middleware to manage request flow

proxy: remove duplicate error handling in New
proxy: remove routeConfigs in favor of using gorilla/mux
proxy: add proxy specific middleware
proxy: no longer need to use middleware / handler to check if valid route. Can use build in 404 mux.
internal/middleware: add cors bypass middleware

Signed-off-by: Bobby DeSimone <bobbydesimone@gmail.com>

internal/httputil/proxy_test.go

@@ -0,0 +1,35 @@
+package httputil // import "github.com/pomerium/pomerium/internal/httputil"
+
+import (
+	"io/ioutil"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+)
+
+func TestNewReverseProxy(t *testing.T) {
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		hostname, _, _ := net.SplitHostPort(r.Host)
+		w.Write([]byte(hostname))
+	}))
+	defer backend.Close()
+
+	backendURL, _ := url.Parse(backend.URL)
+	backendHostname, backendPort, _ := net.SplitHostPort(backendURL.Host)
+	backendHost := net.JoinHostPort(backendHostname, backendPort)
+	proxyURL, _ := url.Parse(backendURL.Scheme + "://" + backendHost + "/")
+
+	proxyHandler := NewReverseProxy(proxyURL)
+	frontend := httptest.NewServer(proxyHandler)
+	defer frontend.Close()
+
+	getReq, _ := http.NewRequest("GET", frontend.URL, nil)
+	res, _ := http.DefaultClient.Do(getReq)
+	bodyBytes, _ := ioutil.ReadAll(res.Body)
+	if g, e := string(bodyBytes), backendHostname; g != e {
+		t.Errorf("got body %q; expected %q", g, e)
+	}
+}