Plugins: Automatically forward plugin request HTTP headers in outgoing HTTP requests (#60417)

Automatically forward core plugin request HTTP headers in outgoing HTTP requests. 
Core datasource plugin authors don't have to specifically handle forwarding of HTTP 
headers, e.g. do not have to "hardcode" the header-names in the datasource plugin, 
if not having custom needs.

Fixes #57065

pkg/services/pluginsintegration/clientmiddleware/httpclient_middleware.go

@@ -0,0 +1,108 @@
+package clientmiddleware
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana-plugin-sdk-go/backend/httpclient"
+	"github.com/grafana/grafana/pkg/plugins"
+	ngalertmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
+)
+
+const forwardPluginRequestHTTPHeaders = "forward-plugin-request-http-headers"
+
+// NewHTTPClientMiddleware creates a new plugins.ClientMiddleware
+// that will forward plugin request headers as outgoing HTTP headers.
+func NewHTTPClientMiddleware() plugins.ClientMiddleware {
+	return plugins.ClientMiddlewareFunc(func(next plugins.Client) plugins.Client {
+		return &HTTPClientMiddleware{
+			next: next,
+		}
+	})
+}
+
+type HTTPClientMiddleware struct {
+	next plugins.Client
+}
+
+func (m *HTTPClientMiddleware) applyHeaders(ctx context.Context, pReq interface{}) context.Context {
+	if pReq == nil {
+		return ctx
+	}
+
+	mw := httpclient.NamedMiddlewareFunc(forwardPluginRequestHTTPHeaders, func(opts httpclient.Options, next http.RoundTripper) http.RoundTripper {
+		return httpclient.RoundTripperFunc(func(req *http.Request) (*http.Response, error) {
+			switch t := pReq.(type) {
+			case *backend.QueryDataRequest:
+				if val, exists := t.Headers[ngalertmodels.FromAlertHeaderName]; exists {
+					req.Header.Set(ngalertmodels.FromAlertHeaderName, val)
+				}
+			case *backend.CallResourceRequest:
+				if val, exists := t.Headers[ngalertmodels.FromAlertHeaderName]; exists {
+					req.Header.Set(ngalertmodels.FromAlertHeaderName, val[0])
+				}
+			case *backend.CheckHealthRequest:
+				if val, exists := t.Headers[ngalertmodels.FromAlertHeaderName]; exists {
+					req.Header.Set(ngalertmodels.FromAlertHeaderName, val)
+				}
+			}
+
+			if h, ok := pReq.(backend.ForwardHTTPHeaders); ok {
+				for k, v := range h.GetHTTPHeaders() {
+					req.Header[k] = v
+				}
+			}
+
+			return next.RoundTrip(req)
+		})
+	})
+
+	return httpclient.WithContextualMiddleware(ctx, mw)
+}
+
+func (m *HTTPClientMiddleware) QueryData(ctx context.Context, req *backend.QueryDataRequest) (*backend.QueryDataResponse, error) {
+	if req == nil {
+		return m.next.QueryData(ctx, req)
+	}
+
+	ctx = m.applyHeaders(ctx, req)
+
+	return m.next.QueryData(ctx, req)
+}
+
+func (m *HTTPClientMiddleware) CallResource(ctx context.Context, req *backend.CallResourceRequest, sender backend.CallResourceResponseSender) error {
+	if req == nil {
+		return m.next.CallResource(ctx, req, sender)
+	}
+
+	ctx = m.applyHeaders(ctx, req)
+
+	return m.next.CallResource(ctx, req, sender)
+}
+
+func (m *HTTPClientMiddleware) CheckHealth(ctx context.Context, req *backend.CheckHealthRequest) (*backend.CheckHealthResult, error) {
+	if req == nil {
+		return m.next.CheckHealth(ctx, req)
+	}
+
+	ctx = m.applyHeaders(ctx, req)
+
+	return m.next.CheckHealth(ctx, req)
+}
+
+func (m *HTTPClientMiddleware) CollectMetrics(ctx context.Context, req *backend.CollectMetricsRequest) (*backend.CollectMetricsResult, error) {
+	return m.next.CollectMetrics(ctx, req)
+}
+
+func (m *HTTPClientMiddleware) SubscribeStream(ctx context.Context, req *backend.SubscribeStreamRequest) (*backend.SubscribeStreamResponse, error) {
+	return m.next.SubscribeStream(ctx, req)
+}
+
+func (m *HTTPClientMiddleware) PublishStream(ctx context.Context, req *backend.PublishStreamRequest) (*backend.PublishStreamResponse, error) {
+	return m.next.PublishStream(ctx, req)
+}
+
+func (m *HTTPClientMiddleware) RunStream(ctx context.Context, req *backend.RunStreamRequest, sender *backend.StreamSender) error {
+	return m.next.RunStream(ctx, req, sender)
+}