Ansible role to push deploy key onto Gitlab instance

deployer_defaults_main.yml

---
deployer_user: deploy
deployer_group: deploy
deployer_groups: ['admin']
deployer_user_ssh_key_file: .ssh/id_rsa
deployer_gitlab_api: https://[gitlab-domain]/api/v3/
deployer_gitlab_token: [gitlab-token-for-specific-user]
deployer_gitlab_key_title: "{{ ansible_hostname }}_deployer"

deployer_tasks_main.yml

---
- name: Create deployer group
  group: name={{ deployer_group }} state=present

- name: Create deployer user and generate a ssh key
  user: name={{ deployer_user }}
        group={{ deployer_group }}
        groups={{ deployer_groups | join(',') }}
        state=present
        shell=/bin/bash
        generate_ssh_key=yes
        ssh_key_type=rsa
        ssh_key_file="{{ deployer_user_ssh_key_file }}"
  register: deploy_user_created


- name: Assign ssh key to a variable
  shell:
    cat /home/{{ deployer_user }}/{{ deployer_user_ssh_key_file }}.pub
  register: deployer_user_public_key
  when: deploy_user_created.changed

- name: Push the generated ssh key to the Gitlab instance
  uri: >
      url="{{ deployer_gitlab_api }}user/keys"
      method=POST
      status_code=201
      HEADER_PRIVATE-TOKEN="{{ deployer_gitlab_token }}"
      HEADER_Content-Type="application/json"
      body="{\"title\": \"{{ deployer_gitlab_key_title }}\", \"key\": \"{{ deployer_user_public_key.stdout_lines.0 }}\"}"
  when: deploy_user_created.changed

- name: Ensure .ssh/config file exists
  file: state=touch path="/home/{{ deployer_user }}/.ssh/config"

- name: Disable host key checking
  lineinfile: dest=/home/{{ deployer_user }}/.ssh/config line='Host *\n \tStrictHostKeyChecking no\n\tUserKnownHostsFile=/dev/null'

- name: Add deploy group to sudoers file and validate
  lineinfile: dest=/etc/sudoers state=present regexp='^%{{ deployer_group }}' line='%{{ deployer_group }} ALL=(ALL) NOPASSWD:ALL' validate="visudo -cf %s"

 name: Push the generated ssh key to the Gitlab Deploy Keys
  uri: >
      url="{{ deployer_gitlab_api }}projects/{{ repo_project_id }}/keys"
      return_content=yes
      body_format=json
      method=POST
      status_code=201,200,304,400,401,403,404,405,409,422,500
      HEADER_PRIVATE-TOKEN="{{ deployer_gitlab_token }}"
      body="{{ data_json_push.stdout_lines.0 }}"
  when: deployer_use_deploy_key == false

You can't use newlines like this in yaml. Try this instead (the ">" indicates that the next lines are to be concatenated):

Create an item via API

- uri: >
    url="http://www.myapi.com/create"
    method=POST return_content=yes HEADER_Content-Type="application/json"
    body="{{ lookup('file','create_body.json') | to_json }}"

But I find this much better:

Create an item via API

- uri: 
    url: "http://www.myapi.com/create"
    method: POST
    return_content: yes
    HEADER_Content-Type: "application/json"
    body: "{{ lookup('file','create_body.json') | to_json }}"