Getting a file based on a variable in Ansible

create_ssh_user.yml

---

############################################################
# The lookup on line 9 is currenlty failing.
# Can anyone recommend how I can achieve the following?
# Is there a better way to go about doing what I've set out  to do here?
############################################################

- name: Add user {{ user }}
  user: name={{user}}

- name: Add keys for user {{ user }}
  authorized_key: user={{ user }} key="{{ lookup('file', user +'.txt') }}"
    manage_dir=yes state=present unique=yes