Alerting: add field for custom slack endpoint (#45751)

* add field for custom slack endpoint

* add test for using custom endpoint

* Update pkg/services/ngalert/notifier/channels/slack.go

Co-authored-by: Alexander Weaver <weaver.alex.d@gmail.com>

* specify description for endpoint

* remove brittle string constants

Co-authored-by: Alexander Weaver <weaver.alex.d@gmail.com>

pkg/services/ngalert/notifier/available_channels.go

@@ -459,6 +459,14 @@ func GetAvailableNotifiers() []*alerting.NotifierPlugin {
 					PropertyName: "url",
 					Secure:       true,
 				},
+				{ // New in 8.4.
+					Label:        "Endpoint URL",
+					Element:      alerting.ElementTypeInput,
+					InputType:    alerting.InputTypeText,
+					Description:  "Optionally provide a custom Slack message API endpoint for non-webhook requests, default is https://slack.com/api/chat.postMessage",
+					Placeholder:  "Slack endpoint url",
+					PropertyName: "endpointUrl",
+				},
 				{ // New in 8.0.
 					Label:        "Title",
 					Element:      alerting.ElementTypeInput,

pkg/services/ngalert/notifier/channels/slack.go

@@ -52,9 +52,11 @@ func NewSlackNotifier(model *NotificationChannelConfig, t *template.Template, fn
 		return nil, receiverInitError{Cfg: *model, Reason: "no secure settings supplied"}
 	}
 
+	endpointURL := model.Settings.Get("endpointUrl").MustString(SlackAPIEndpoint)
+
 	slackURL := fn(context.Background(), model.SecureSettings, "url", model.Settings.Get("url").MustString())
 	if slackURL == "" {
-		slackURL = SlackAPIEndpoint
+		slackURL = endpointURL
 	}
 	apiURL, err := url.Parse(slackURL)
 	if err != nil {
@@ -62,7 +64,7 @@ func NewSlackNotifier(model *NotificationChannelConfig, t *template.Template, fn
 	}
 
 	recipient := strings.TrimSpace(model.Settings.Get("recipient").MustString())
-	if recipient == "" && apiURL.String() == SlackAPIEndpoint {
+	if recipient == "" && apiURL.String() == endpointURL {
 		return nil, receiverInitError{Cfg: *model,
 			Reason: "recipient must be specified when using the Slack chat API",
 		}

pkg/services/ngalert/notifier/channels/slack_test.go

@@ -160,6 +160,42 @@ func TestSlackNotifier(t *testing.T) {
 			}`,
 			expInitError: `failed to validate receiver "slack_testing" of type "slack": recipient must be specified when using the Slack chat API`,
 		},
+		{
+			name: "Custom endpoint url",
+			settings: `{
+				"token": "1234",
+				"recipient": "#testchannel",
+				"endpointUrl": "https://slack-custom.com/api/",
+				"icon_emoji": ":emoji:"
+			}`,
+			alerts: []*types.Alert{
+				{
+					Alert: model.Alert{
+						Labels:      model.LabelSet{"alertname": "alert1", "lbl1": "val1"},
+						Annotations: model.LabelSet{"ann1": "annv1"},
+					},
+				},
+			},
+			expMsg: &slackMessage{
+				Channel:   "#testchannel",
+				Username:  "Grafana",
+				IconEmoji: ":emoji:",
+				Attachments: []attachment{
+					{
+						Title:      "[FIRING:1]  (val1)",
+						TitleLink:  "http://localhost/alerting/list",
+						Text:       "**Firing**\n\nValue: [no value]\nLabels:\n - alertname = alert1\n - lbl1 = val1\nAnnotations:\n - ann1 = annv1\nSilence: http://localhost/alerting/silence/new?alertmanager=grafana&matchers=alertname%3Dalert1%2Clbl1%3Dval1\n",
+						Fallback:   "[FIRING:1]  (val1)",
+						Fields:     nil,
+						Footer:     "Grafana v" + setting.BuildVersion,
+						FooterIcon: "https://grafana.com/assets/img/fav32.png",
+						Color:      "#D63232",
+						Ts:         0,
+					},
+				},
+			},
+			expMsgError: nil,
+		},
 	}
 
 	for _, c := range cases {
@@ -196,6 +232,12 @@ func TestSlackNotifier(t *testing.T) {
 					_ = request.Body.Close()
 				}()
 
+				url := settingsJSON.Get("url").MustString()
+				if len(url) == 0 {
+					endpointUrl := settingsJSON.Get("endpointUrl").MustString(SlackAPIEndpoint)
+					require.Equal(t, endpointUrl, request.URL.String())
+				}
+
 				b, err := io.ReadAll(request.Body)
 				require.NoError(t, err)
 				body = string(b)