Refactor routers directory (#15800)

* refactor routers directory

* move func used for web and api to common

* make corsHandler a function to prohibit side efects

* rm unused func

Co-authored-by: 6543 <6543@obermui.de>

routers/web/metrics.go

@@ -0,0 +1,34 @@
+// Copyright 2018 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package web
+
+import (
+	"crypto/subtle"
+	"net/http"
+
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+// Metrics validate auth token and render prometheus metrics
+func Metrics(resp http.ResponseWriter, req *http.Request) {
+	if setting.Metrics.Token == "" {
+		promhttp.Handler().ServeHTTP(resp, req)
+		return
+	}
+	header := req.Header.Get("Authorization")
+	if header == "" {
+		http.Error(resp, "", 401)
+		return
+	}
+	got := []byte(header)
+	want := []byte("Bearer " + setting.Metrics.Token)
+	if subtle.ConstantTimeCompare(got, want) != 1 {
+		http.Error(resp, "", 401)
+		return
+	}
+	promhttp.Handler().ServeHTTP(resp, req)
+}