tasks in a role, current solution and approximated solution

1current.yaml

- name: See if authentication is enabled in mongod.conf
  check_mode: yes
  lineinfile:
    path: /etc/mongod.conf
    insertafter: 'security:'
    line: '  authorization: enabled'
  register: mongo_authorization

- name: Add mongo admin when authorization is disabled
  mongodb_user:
    state: present
    update_password: on_create
    
    name: "{{ st2mongo_admin_username }}"
    password: "{{ st2mongo_admin_password }}"
    database: "{{ st2mongo_admin_db }}"
    roles: userAdminAnyDatabase

    login_host: "{{ st2mongo_host }}"
    login_port: "{{ st2mongo_port }}"
    login_user: "{{ st2mongo_admin_username }}"
    login_password: "{{ st2mongo_admin_password }}"
  when: mongo_authorization|changed

- name: Make sure mongo admin is setup when authorization is enabled
  mongodb_user:
    state: present
    update_password: on_create

    name: "{{ st2mongo_admin_username }}"
    password: "{{ st2mongo_admin_password }}"
    database: "{{ st2mongo_admin_db }}"
    roles: userAdminAnyDatabase

    login_host: "{{ st2mongo_host }}"
    login_port: "{{ st2mongo_port }}"
  notify: Restart mongod
  when: mongo_authorization|succeeded

2wanted.yaml

- name: See if authentication is enabled in mongod.conf
  check_mode: yes
  lineinfile:
    path: /etc/mongod.conf
    insertafter: 'security:'
    line: '  authorization: enabled'
  register: mongo_authorization

- name: Add mongo admin
  mongodb_user:
    state: present
    update_password: on_create
    
    name: "{{ st2mongo_admin_username }}"
    password: "{{ st2mongo_admin_password }}"
    database: "{{ st2mongo_admin_db }}"
    roles: userAdminAnyDatabase

    login_host: "{{ st2mongo_host }}"
    login_port: "{{ st2mongo_port }}"
    login_user: "{{ if mongo_authorization|changed then st2mongo_admin_username or omit}}"
    login_password: "{{ mongo_authorization|changed then st2mongo_admin_password or omit }}"

3finished.yaml

- name: See if authorization is enabled in mongod.conf
  check_mode: yes
  lineinfile:
    path: /etc/mongod.conf
    insertafter: 'security:'
    line: '  authorization: enabled'
  register: mongo_authorization
  # changed = line not in file, authorization is disabled
  # succeeded = line in file, authorization is enabled

- name: Add mongo admin
  mongodb_user:
    state: present
    update_password: on_create

    name: "{{ st2mongo_admin_username }}"
    password: "{{ st2mongo_admin_password }}"
    database: "{{ st2mongo_admin_db }}"
    roles: userAdminAnyDatabase

    login_host: "{{ st2mongo_host }}"
    login_port: "{{ st2mongo_port }}"
    login_user: "{{ mongo_authorization|changed | ternary(omit, st2mongo_admin_username) }}"
    login_password: "{{ mongo_authorization|changed | ternary(omit, st2mongo_admin_password) }}"