Refactor Webhook + Add X-Hub-Signature (#16176)

This PR removes multiple unneeded fields from the `HookTask` struct and adds the two headers `X-Hub-Signature` and `X-Hub-Signature-256`.

## ⚠️ BREAKING ⚠️ 

* The `Secret` field is no longer passed as part of the payload.
* "Breaking" change (or fix?): The webhook history shows the real called url and not the url registered in the webhook (`deliver.go`@129).

Close #16115
Fixes #7788
Fixes #11755

Co-authored-by: zeripath <art27@cantab.net>

models/migrations/migrations.go

@@ -323,6 +323,8 @@ var migrations = []Migration{
 	NewMigration("Add new table repo_archiver", addRepoArchiver),
 	// v186 -> v187
 	NewMigration("Create protected tag table", createProtectedTagTable),
+	// v187 -> v188
+	NewMigration("Drop unneeded webhook related columns", dropWebhookColumns),
 }
 
 // GetCurrentDBVersion returns the current db version

models/migrations/v187.go

@@ -0,0 +1,46 @@
+// Copyright 2021 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 migrations
+
+import (
+	"xorm.io/xorm"
+)
+
+func dropWebhookColumns(x *xorm.Engine) error {
+	// Make sure the columns exist before dropping them
+	type Webhook struct {
+		Signature string `xorm:"TEXT"`
+		IsSSL     bool   `xorm:"is_ssl"`
+	}
+	if err := x.Sync2(new(Webhook)); err != nil {
+		return err
+	}
+
+	type HookTask struct {
+		Typ         string `xorm:"VARCHAR(16) index"`
+		URL         string `xorm:"TEXT"`
+		Signature   string `xorm:"TEXT"`
+		HTTPMethod  string `xorm:"http_method"`
+		ContentType int
+		IsSSL       bool
+	}
+	if err := x.Sync2(new(HookTask)); err != nil {
+		return err
+	}
+
+	sess := x.NewSession()
+	defer sess.Close()
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+	if err := dropTableColumns(sess, "webhook", "signature", "is_ssl"); err != nil {
+		return err
+	}
+	if err := dropTableColumns(sess, "hook_task", "typ", "url", "signature", "http_method", "content_type", "is_ssl"); err != nil {
+		return err
+	}
+
+	return sess.Commit()
+}