How add meta fields to a user with the wp-api?

I have managed to do this with hooking into rest_insert_user.
I send an array like this:

var data = {
       first_name: user.first_name,
       last_name: user.last_name,
       name: user.display_name,
       email: user.email,
       description: user.description,
       meta: {
        'wpcf-phone': user.phone,
        'wpcf-institution': user.institution,
        'wpcf-birthday': Math.round(new Date(user.birthday).getTime()/1000)
      }
   };

And treat only the meta data through the hook as this:

function aa_user_update($user, $request, $create)
{
    if ($request['meta']) {
        $user_id = $user->ID;
        foreach ($request['meta'] as $key => $value) {
            update_user_meta( $user_id, $key, $value );
        }
    }
}
add_action( 'rest_insert_user', 'aa_user_update', 12, 3 );

The ordinary fields of the user are updated normally by the API.