Docker CE: Install Docker credential helpers.

Installation is optional and can be turned off by setting variable
`docker_credential_helpers_release` to 0.

docs/playbooks.rst

@@ -1313,6 +1313,13 @@ The following variables may be set to alter the role behavior:
        set it to 0 or the empty string to skip installing ``docker-compose``.
 
        .. __: https://github.com/docker/compose/releases
+   * - ``docker_credential_helpers_release``
+     - ``v0.6.3``
+     - What `release of *Docker credential helpers*`__ to install;
+       set it to 0 or the empty string to skip installing them.  Note that
+       all release tags start with the letter ``v`` (as of April 2020).
+
+       .. __: https://github.com/docker/docker-credential-helpers/releases/
    * - ``docker_group_members``
      - ``[]``
      - List of users that are authorized to call the ``docker``

elasticluster/share/playbooks/roles/docker-ce/defaults/main.yml

@@ -16,3 +16,6 @@ docker_prune_frequency: 'daily'
 # set it to `null` to skip installing `docker-compose`
 docker_compose_release: '1.25.5'
 
+# What release of the Docker credential helpers to install;
+# set it to `null` to skip installing them
+docker_credential_helpers_release: 'v0.6.3'

elasticluster/share/playbooks/roles/docker-ce/tasks/main.yml

@@ -62,6 +62,29 @@
     mode: 'u+rwx,g+rx'
   when: 'docker_compose_release|bool'
 
+
+- name: 'Install Docker credential helpers'
+  unarchive:
+    src: 'https://github.com/docker/docker-credential-helpers/releases/download/{{ docker_credential_helpers_release }}/docker-credential-{{ item }}-{{ docker_credential_helpers_release }}-amd64.tar.gz'
+    dest: '/usr/local/bin/'
+    remote_src: yes
+    group: 'docker'
+    mode: 'u+rwx,g+rx'
+  loop:
+    - pass
+    - secretservice
+  when: 'docker_credential_helpers_release|bool'
+
+
+- name: 'Install dependencies of Docker credential helpers'
+  package:
+    name:
+      - 'pass'
+      - 'gnupg2'
+    state: '{{ pkg_install_state }}'
+  when: 'docker_credential_helpers_release|bool'
+
+
 - name: 'Enable Docker service and ensure it (re)starts at boot'
   service:
     name: 'docker'