"invalid key specified: lookup( 'file', 'sources/keys/newUser.pub') }}"}

add-dev-user.yml

$ cat sources/keys/newUser.pub 
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDRxc4tyOZ8dPM6O3NPWcZjk9KZRdNEbOfHwvSptBk7wCs8WqzRaNoAY4Al3ZERSwjSr7yhz4NkJSw6xaX+MzkKkQboLglsDoZTCVh44uOPOGU2K8zKwuu5YxdkbpFVF5M6tzD625dMvpZf91qj+l9ViizoRqI+WzdYRqxYnqtfL+jUygvIZ4wakucxKsM1T+aKe4K+JzoAGPfSssIZO0l0nTVmmpOx83CKeXWZRv2GK5KvsrzQFGdTBlewvI9LLurUxQ4y5Iu9rWAB2KA97QPgLQlVqogUeTTmdRYf1tUzXMB/C4oWl1oeiEKFpndybXotgP3gnoyjUshOYaxjEibj newUser@host
--------------------------------------------------------------------------------

- hosts: host_group
  become: yes
  become_method: sudo
  tasks:
    - name: add development user to the system
      user: name=newUser comment="GECOS" uid=1013 groups=wheel
    - name: injecting users public ssh key into remote authorized_keys file
      authorized_key:
        user: newUser
        #key:  sources/keys/newUser.pub
        key:  "lookup( 'file', 'sources/keys/newUser.pub') }}"
        state: present
        exclusive: yes
--------------------------------------------------------------------------------

$ ansible-playbook add-dev-user.yml 

PLAY [safworx-dev] *************************************************************

TASK [setup] *******************************************************************
ok: [safworx.fbfs.com]

TASK [add development user to the system] **************************************
ok: [safworx.fbfs.com]

TASK [injecting users public ssh key into remote authorized_keys file] *********
fatal: [safworx.fbfs.com]: FAILED! => {"changed": false, "failed": true, "msg": "invalid key specified: lookup( 'file', 'sources/keys/newUser.pub') }}"}

NO MORE HOSTS LEFT *************************************************************
	to retry, use: --limit @add-dev-user.retry

PLAY RECAP *********************************************************************
safworx.fbfs.com           : ok=2    changed=0    unreachable=0    failed=1   

--------------------------------------------------------------------------------

$ file sources/keys/newUser.pub 
sources/keys/newUser.pub: OpenSSH RSA public key