Loki: Allow alert headers to be forwarded (#90890)

* Loki: Allow alert headers to be forwarded

* Loki: fix tests

---------

Co-authored-by: Yuri Tseretyan <yuriy.tseretyan@grafana.com>

pkg/services/ngalert/eval/eval.go

@@ -334,7 +334,7 @@ func buildDatasourceHeaders(ctx context.Context, metadata map[string]string) map
 	headers := make(map[string]string, len(metadata)+3)
 
 	for key, value := range metadata {
-		headers[fmt.Sprintf("X-Rule-%s", key)] = url.QueryEscape(value)
+		headers[fmt.Sprintf("http_X-Rule-%s", key)] = url.QueryEscape(value)
 	}
 
 	// Many data sources check this in query method as sometimes alerting needs special considerations.

pkg/services/ngalert/eval/eval_test.go

@@ -1262,9 +1262,9 @@ func TestCreate(t *testing.T) {
 		}
 
 		expectedHeaders := map[string]string{
-			"X-Rule-Test1":             "data1",
-			"X-Rule-Test2":             "%D0%BC%D1%83%D0%B7%D1%8B%D0%BA%D0%B0+%F0%9F%8E%B6",
-			"X-Rule-Test3":             "",
+			"http_X-Rule-Test1":        "data1",
+			"http_X-Rule-Test2":        "%D0%BC%D1%83%D0%B7%D1%8B%D0%BA%D0%B0+%F0%9F%8E%B6",
+			"http_X-Rule-Test3":        "",
 			models.FromAlertHeaderName: "true",
 			models.CacheSkipHeaderName: "true",
 			"X-Grafana-Org-Id":         strconv.FormatInt(orgID, 10),

pkg/tsdb/loki/loki.go

@@ -90,6 +90,7 @@ func newInstanceSettings(httpClientProvider *httpclient.Provider) datasource.Ins
 		if err != nil {
 			return nil, err
 		}
+		opts.ForwardHTTPHeaders = true
 
 		client, err := httpClientProvider.New(opts)
 		if err != nil {