Webhook support custom proxy (#8760)

* Webhook support custom proxy

* Add glob support on webhook proxy host rules

* fix app.ini.sample

* improve code and app.ini.sample

* update cheetsheet about added webhook options

modules/webhook/deliver_test.go

@@ -0,0 +1,39 @@
+// Copyright 2019 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 webhook
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+
+	"code.gitea.io/gitea/modules/setting"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestWebhookProxy(t *testing.T) {
+	setting.Webhook.ProxyURL = "http://localhost:8080"
+	setting.Webhook.ProxyURLFixed, _ = url.Parse(setting.Webhook.ProxyURL)
+	setting.Webhook.ProxyHosts = []string{"*.discordapp.com", "discordapp.com"}
+
+	var kases = map[string]string{
+		"https://discordapp.com/api/webhooks/xxxxxxxxx/xxxxxxxxxxxxxxxxxxx": "http://localhost:8080",
+		"http://s.discordapp.com/assets/xxxxxx":                             "http://localhost:8080",
+		"http://github.com/a/b":                                             "",
+	}
+
+	for reqURL, proxyURL := range kases {
+		req, err := http.NewRequest("POST", reqURL, nil)
+		assert.NoError(t, err)
+
+		u, err := webhookProxy()(req)
+		assert.NoError(t, err)
+		if proxyURL == "" {
+			assert.Nil(t, u)
+		} else {
+			assert.EqualValues(t, proxyURL, u.String())
+		}
+	}
+}