vendor: update buildkit to f238f1e

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/moby/buildkit/session/auth/authprovider/authprovider.go

@@ -2,7 +2,8 @@ package authprovider
 
 import (
 	"context"
-	"io/ioutil"
+	"io"
+	"sync"
 
 	"github.com/docker/cli/cli/config"
 	"github.com/docker/cli/cli/config/configfile"
@@ -11,14 +12,20 @@ import (
 	"google.golang.org/grpc"
 )
 
-func NewDockerAuthProvider() session.Attachable {
+func NewDockerAuthProvider(stderr io.Writer) session.Attachable {
 	return &authProvider{
-		config: config.LoadDefaultConfigFile(ioutil.Discard),
+		config: config.LoadDefaultConfigFile(stderr),
 	}
 }
 
 type authProvider struct {
 	config *configfile.ConfigFile
+
+	// The need for this mutex is not well understood.
+	// Without it, the docker cli on OS X hangs when
+	// reading credentials from docker-credential-osxkeychain.
+	// See issue https://github.com/docker/cli/issues/1862
+	mu sync.Mutex
 }
 
 func (ap *authProvider) Register(server *grpc.Server) {
@@ -26,6 +33,8 @@ func (ap *authProvider) Register(server *grpc.Server) {
 }
 
 func (ap *authProvider) Credentials(ctx context.Context, req *auth.CredentialsRequest) (*auth.CredentialsResponse, error) {
+	ap.mu.Lock()
+	defer ap.mu.Unlock()
 	if req.Host == "registry-1.docker.io" {
 		req.Host = "https://index.docker.io/v1/"
 	}