client: add staticAuth utility

Add a small utility to create a "RequestAuthConfig" from
a static value.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

client/auth.go

@@ -0,0 +1,14 @@
+package client
+
+import (
+	"context"
+
+	"github.com/docker/docker/api/types/registry"
+)
+
+// staticAuth creates a privilegeFn from the given registryAuth.
+func staticAuth(registryAuth string) registry.RequestAuthConfig {
+	return func(ctx context.Context) (string, error) {
+		return registryAuth, nil
+	}
+}