Move Logging to Middleware Package (#1070)

* Use a specialized ResponseWriter in middleware

* Track User & Upstream in RequestScope

* Wrap responses in our custom ResponseWriter

* Add tests for logging middleware

* Inject upstream metadata into request scope

* Use custom ResponseWriter only in logging middleware

* Assume RequestScope is never nil

pkg/middleware/middleware_suite_test.go

@@ -4,6 +4,7 @@ import (
 	"net/http"
 	"testing"
 
+	middlewareapi "github.com/oauth2-proxy/oauth2-proxy/v7/pkg/apis/middleware"
 	"github.com/oauth2-proxy/oauth2-proxy/v7/pkg/logger"
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
@@ -19,6 +20,17 @@ func TestMiddlewareSuite(t *testing.T) {
 
 func testHandler() http.Handler {
 	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		rw.WriteHeader(200)
+		rw.Write([]byte("test"))
+	})
+}
+
+func testUpstreamHandler(upstream string) http.Handler {
+	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		scope := middlewareapi.GetRequestScope(req)
+		scope.Upstream = upstream
+
+		rw.WriteHeader(200)
 		rw.Write([]byte("test"))
 	})
 }