Ensure that datasource apiservers receive and forwards headers (#92304)

* Ensure that datasource apiservers receive and forwards headers for datasources:
- adds log line for prometheus to see when from alert header is received
- add logging to the datasource apiserver
- Updates the Connect func in sub query to forward expected headers to datasources and log unexpected ones.

pkg/registry/apis/datasource/sub_query_test.go

@@ -0,0 +1,98 @@
+package datasource
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/grafana/grafana-plugin-sdk-go/backend"
+	"github.com/grafana/grafana/pkg/apis/datasource/v0alpha1"
+	"github.com/grafana/grafana/pkg/infra/log"
+	"github.com/stretchr/testify/require"
+	"k8s.io/apimachinery/pkg/runtime"
+)
+
+func TestSubQueryConnect(t *testing.T) {
+	sqr := subQueryREST{
+		builder: &DataSourceAPIBuilder{
+			client: mockClient{
+				lastCalledWithHeaders: &map[string]string{},
+			},
+			datasources:     mockDatasources{},
+			contextProvider: mockContextProvider{},
+			log:             log.NewNopLogger(),
+		},
+	}
+
+	mr := mockResponder{}
+	handler, err := sqr.Connect(context.Background(), "dsname", nil, mr)
+	require.NoError(t, err)
+
+	rr := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/some-path", nil)
+	req.Header.Set("fromAlert", "true")
+	req.Header.Set("Content-Type", "application/json")
+	handler.ServeHTTP(rr, req)
+
+	// test that headers are forwarded and cased appropriately
+	require.Equal(t, map[string]string{
+		"FromAlert":    "true",
+		"Content-Type": "application/json",
+	}, *sqr.builder.client.(mockClient).lastCalledWithHeaders)
+}
+
+type mockClient struct {
+	lastCalledWithHeaders *map[string]string
+}
+
+func (m mockClient) QueryData(ctx context.Context, req *backend.QueryDataRequest) (*backend.QueryDataResponse, error) {
+	*m.lastCalledWithHeaders = req.Headers
+	return nil, fmt.Errorf("mock error")
+}
+
+func (m mockClient) CallResource(ctx context.Context, req *backend.CallResourceRequest, sender backend.CallResourceResponseSender) error {
+	return nil
+}
+
+func (m mockClient) CheckHealth(ctx context.Context, req *backend.CheckHealthRequest) (*backend.CheckHealthResult, error) {
+	return nil, nil
+}
+
+type mockResponder struct {
+}
+
+// Object writes the provided object to the response. Invoking this method multiple times is undefined.
+func (m mockResponder) Object(statusCode int, obj runtime.Object) {
+}
+
+// Error writes the provided error to the response. This method may only be invoked once.
+func (m mockResponder) Error(err error) {
+}
+
+type mockDatasources struct {
+}
+
+// Get gets a specific datasource (that the user in context can see)
+func (m mockDatasources) Get(ctx context.Context, uid string) (*v0alpha1.DataSourceConnection, error) {
+	return nil, nil
+}
+
+// List lists all data sources the user in context can see
+func (m mockDatasources) List(ctx context.Context) (*v0alpha1.DataSourceConnectionList, error) {
+	return nil, nil
+}
+
+// Return settings (decrypted!) for a specific plugin
+// This will require "query" permission for the user in context
+func (m mockDatasources) GetInstanceSettings(ctx context.Context, uid string) (*backend.DataSourceInstanceSettings, error) {
+	return nil, nil
+}
+
+type mockContextProvider struct {
+}
+
+func (m mockContextProvider) PluginContextForDataSource(ctx context.Context, datasourceSettings *backend.DataSourceInstanceSettings) (backend.PluginContext, error) {
+	return backend.PluginContext{}, nil
+}