docs: Docker driver supports task user option

Also, add a test case.

drivers/docker/driver_test.go

@@ -1009,6 +1009,23 @@ func TestDockerDriver_CreateContainerConfig(t *testing.T) {
 	require.Equal(t, containerName, c.Name)
 }
 
+func TestDockerDriver_CreateContainerConfig_User(t *testing.T) {
+	t.Parallel()
+
+	task, cfg, _ := dockerTask(t)
+	task.User = "random-user-1"
+
+	require.NoError(t, task.EncodeConcreteDriverConfig(cfg))
+
+	dh := dockerDriverHarness(t, nil)
+	driver := dh.Impl().(*Driver)
+
+	c, err := driver.createContainerConfig(task, cfg, "org/repo:0.1")
+	require.NoError(t, err)
+
+	require.Equal(t, task.User, c.Config.User)
+}
+
 func TestDockerDriver_CreateContainerConfig_Labels(t *testing.T) {
 	t.Parallel()
 

website/source/docs/drivers/docker.html.md

@@ -413,6 +413,8 @@ The `docker` driver supports the following configuration in the job spec.  Only
 * `pids_limit` - (Optional) An integer value that specifies the pid limit for
   the container. Defaults to unlimited.
 
+Additionally, docker driver supports customization of the container user through task [`user` option](/docs/job-specification/task.html#user).
+
 ### Container Name
 
 Nomad creates a container after pulling an image. Containers are named