PLT-6965 jira integration (plus plugin scaffolding) (#6918)

* plugin scaffolding / jira integration

* add vendored testify packages

* webhook fix

* don't change i18n ids

* support configuration watching

* add basic jira plugin configuration to admin console

* fix eslint errors

* fix another eslint warning

* polish

* undo unintentional config.json commit >:(

* test fix

* add jira plugin diagnostics, remove dm support, add bot tag, generate web-safe secrets

* rebase, implement requested changes

* requested changes

* remove tests and minimize makefile change

* add missing license headers

* add missing comma

* remove bad line from Makefile

app/plugin/jira/plugin.go

@@ -0,0 +1,78 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package jira
+
+import (
+	"crypto/subtle"
+	"encoding/json"
+	"net/http"
+	"sync/atomic"
+
+	l4g "github.com/alecthomas/log4go"
+	"github.com/mattermost/platform/app/plugin"
+	"github.com/mattermost/platform/model"
+)
+
+type Plugin struct {
+	plugin.Base
+	api           plugin.API
+	configuration atomic.Value
+}
+
+func (p *Plugin) Initialize(api plugin.API) {
+	p.api = api
+	p.OnConfigurationChange()
+	api.PluginRouter().HandleFunc("/webhook", p.handleWebhook).Methods("POST")
+}
+
+func (p *Plugin) config() *Configuration {
+	return p.configuration.Load().(*Configuration)
+}
+
+func (p *Plugin) OnConfigurationChange() {
+	var configuration Configuration
+	if err := p.api.LoadPluginConfiguration(&configuration); err != nil {
+		l4g.Error(err.Error())
+	}
+	p.configuration.Store(&configuration)
+}
+
+func (p *Plugin) handleWebhook(w http.ResponseWriter, r *http.Request) {
+	config := p.config()
+	if !config.Enabled || config.Secret == "" || config.UserName == "" {
+		http.Error(w, "This plugin is not configured.", http.StatusForbidden)
+		return
+	} else if subtle.ConstantTimeCompare([]byte(r.URL.Query().Get("secret")), []byte(config.Secret)) != 1 {
+		http.Error(w, "You must provide the configured secret.", http.StatusForbidden)
+		return
+	}
+
+	var webhook Webhook
+
+	if err := json.NewDecoder(r.Body).Decode(&webhook); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+	} else if attachment, err := webhook.SlackAttachment(); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+	} else if attachment == nil {
+		return
+	} else if r.URL.Query().Get("channel") == "" {
+		http.Error(w, "You must provide a channel.", http.StatusBadRequest)
+	} else if user, err := p.api.GetUserByName(config.UserName); err != nil {
+		http.Error(w, p.api.I18n(err.Message, r), err.StatusCode)
+	} else if team, err := p.api.GetTeamByName(r.URL.Query().Get("team")); err != nil {
+		http.Error(w, p.api.I18n(err.Message, r), err.StatusCode)
+	} else if channel, err := p.api.GetChannelByName(team.Id, r.URL.Query().Get("channel")); err != nil {
+		http.Error(w, p.api.I18n(err.Message, r), err.StatusCode)
+	} else if _, err := p.api.CreatePost(&model.Post{
+		ChannelId: channel.Id,
+		Type:      model.POST_SLACK_ATTACHMENT,
+		UserId:    user.Id,
+		Props: map[string]interface{}{
+			"from_webhook": "true",
+			"attachments":  []*model.SlackAttachment{attachment},
+		},
+	}, channel.TeamId); err != nil {
+		http.Error(w, p.api.I18n(err.Message, r), err.StatusCode)
+	}
+}