diff --git a/roles/common/tasks/main.yml b/roles/common/tasks/main.yml
index 5c08716f0dcad4317739488fb59cc1176753bb71..b173a4058f7808c386cbacaa7a8e47e65fcde973 100644
--- a/roles/common/tasks/main.yml
+++ b/roles/common/tasks/main.yml
@@ -30,23 +30,23 @@
   with_items: common_packages
 
 - name: Set-up operating system groups
-  group: name="{{ item.name }}" gid="{{ item.gid }}" state=present
+  group: name="{{ item.name }}" gid="{{ item.gid | default(omit) }}" state=present
   with_items: os_groups
 
 - name: Set-up operating system user groups
-  group: name="{{ item.name }}" gid="{{ item.uid }}" state=present
+  group: name="{{ item.name }}" gid="{{ item.uid | default(omit) }}" state=present
   with_items: os_users
 
 - name: Set-up operating system users
-  user: name="{{ item.name }}" uid="{{ item.uid }}" group="{{ item.name }}"
-        groups="{{ item.additional_groups }}" append=yes shell=/bin/bash state=present
-        password="{{ item.password }}"
+  user: name="{{ item.name }}" uid="{{ item.uid | default(omit) }}" group="{{ item.name }}"
+        groups="{{ ",".join(item.additional_groups | default([])) }}" append=yes shell=/bin/bash state=present
+        password="{{ item.password | default('!') }}"
   with_items: os_users
 
 - name: Set-up authorised keys
   authorized_key: user="{{ item.0.name }}" key="{{ item.1 }}"
   with_subelements:
-    - os_users
+    - "{{ os_users | selectattr('authorized_keys', 'defined') | list }}"
     - authorized_keys
 
 - name: Disable remote logins for root