Add explicit deadline for auth request

An explicit timeout is passed to the handler and a new unit test
proves that the functionality is in place. A additional return
statement was needed in the handler as pointed out by
@stefanprodan.

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

gateway/handlers/external_auth.go

@@ -1 +1,37 @@
 package handlers
+
+import (
+	"context"
+	"net/http"
+	"time"
+)
+
+// MakeExternalAuthHandler make an authentication proxy handler
+func MakeExternalAuthHandler(next http.HandlerFunc, upstreamTimeout time.Duration, upstreamURL string, passBody bool) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		req, _ := http.NewRequest(http.MethodGet, upstreamURL, nil)
+
+		deadlineContext, cancel := context.WithDeadline(
+			context.Background(),
+			time.Now().Add(upstreamTimeout))
+
+		defer cancel()
+
+		res, err := http.DefaultClient.Do(req.WithContext(deadlineContext))
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+
+		if res.Body != nil {
+			defer res.Body.Close()
+		}
+
+		if res.StatusCode == http.StatusOK {
+			next.ServeHTTP(w, r)
+			return
+		}
+
+		w.WriteHeader(res.StatusCode)
+	}
+}