api: use alerting headers (#95118)

* api: use alerting headers

* improve code, add integration test

* better comment

* fixed test

* merged tests

pkg/services/pluginsintegration/clientmiddleware/usealertingheaders_middleware.go

@@ -0,0 +1,57 @@
+package clientmiddleware
+
+import (
+	"context"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana/pkg/services/contexthandler"
+	ngalertmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
+)
+
+func NewUseAlertHeadersMiddleware() backend.HandlerMiddleware {
+	return backend.HandlerMiddlewareFunc(func(next backend.Handler) backend.Handler {
+		return &UseAlertHeadersMiddleware{
+			BaseHandler: backend.NewBaseHandler(next),
+		}
+	})
+}
+
+type UseAlertHeadersMiddleware struct {
+	backend.BaseHandler
+}
+
+var alertHeaders = []string{
+	"X-Rule-Name",
+	"X-Rule-Folder",
+	"X-Rule-Source",
+	"X-Rule-Type",
+	"X-Rule-Version",
+	ngalertmodels.FromAlertHeaderName,
+}
+
+func applyAlertHeaders(ctx context.Context, req *backend.QueryDataRequest) {
+	reqCtx := contexthandler.FromContext(ctx)
+	if reqCtx == nil || reqCtx.Req == nil {
+		return
+	}
+	incomingHeaders := reqCtx.Req.Header
+
+	for _, key := range alertHeaders {
+		incomingValue := incomingHeaders.Get(key)
+		if incomingValue != "" {
+			// FromAlert must be set directly, because we need
+			// to keep the incorrect capitalization for backwards-compatibility
+			// reasons. otherwise Go would normalize it to "Fromalert"
+			if key == ngalertmodels.FromAlertHeaderName {
+				req.Headers[key] = incomingValue
+			} else {
+				req.SetHTTPHeader(key, incomingValue)
+			}
+		}
+	}
+}
+
+func (m *UseAlertHeadersMiddleware) QueryData(ctx context.Context, req *backend.QueryDataRequest) (*backend.QueryDataResponse, error) {
+	applyAlertHeaders(ctx, req)
+	return m.BaseHandler.QueryData(ctx, req)
+}