[v10.4.x] Prometheus: Prevent duplicate registration of custom header middleware (#85120)

Prometheus: Prevent duplicate registration of custom header middleware (#84860)

* remove dupe middleware

* fix test

(cherry picked from commit c8c372c327)

Co-authored-by: Will Browne <wbrowne@users.noreply.github.com>

pkg/tsdb/prometheus/client/transport.go

@@ -59,7 +59,6 @@ func middlewares(logger log.Logger, httpMethod string) []sdkhttpclient.Middlewar
 	middlewares := []sdkhttpclient.Middleware{
 		// TODO: probably isn't needed anymore and should by done by http infra code
 		middleware.CustomQueryParameters(logger),
-		sdkhttpclient.CustomHeadersMiddleware(),
 	}
 
 	// Needed to control GET vs POST method of the requests

pkg/tsdb/prometheus/client/transport_test.go

@@ -23,7 +23,7 @@ func TestCreateTransportOptions(t *testing.T) {
 		opts, err := CreateTransportOptions(context.Background(), settings, backend.NewLoggerWith("logger", "test"))
 		require.NoError(t, err)
 		require.Equal(t, http.Header{"Foo": []string{"bar"}}, opts.Header)
-		require.Equal(t, 2, len(opts.Middlewares))
+		require.Equal(t, 1, len(opts.Middlewares))
 	})
 
 	t.Run("add azure credentials if configured", func(t *testing.T) {
@@ -44,6 +44,6 @@ func TestCreateTransportOptions(t *testing.T) {
 		ctx := backend.WithGrafanaConfig(context.Background(), cfg)
 		opts, err := CreateTransportOptions(ctx, settings, backend.NewLoggerWith("logger", "test"))
 		require.NoError(t, err)
-		require.Equal(t, 3, len(opts.Middlewares))
+		require.Equal(t, 2, len(opts.Middlewares))
 	})
 }