ansible-role-borg-backup/tasks/03_create_key.yml

---
# In this Play an ssh key pair is created for login to the backup server and secure data transfer.
# If you select: "borgmatic_initialization_repo: true",
# the key will automaticly be added to the authorized_keys on the target system.
# We do not want the possibly existing key to be used/distributed, 
# so a backup-specific (backup/backup.pub) one is created.
- name: Create ssh-key (if neeeded) for {{ borgbackup_user }} 
  tags:
    - install_backup
  block:
    - name: Ensire directory exist
      ansible.builtin.file:
        path: "{{ backup_user_info.home }}/.ssh/"
        state: directory
        mode: "0700"
        owner: "{{ borgbackup_user }}"
        group: "{{ borgbackup_group }}"

    - name: Generate an OpenSSH keypair
      community.crypto.openssh_keypair:
        path: "{{ backup_user_info.home }}/.ssh/backup"
        mode: "0600"
        type: "{{ borg_ssh_key_type }}"
        owner: "{{ borgbackup_user }}"
        group: "{{ borgbackup_group }}"
    
    - name: Set key permission
      ansible.builtin.file:
        path: "{{ backup_user_info.home }}/.ssh/backup.pub"
        mode: "0644"
        owner: "{{ borgbackup_user }}"
        group: "{{ borgbackup_group }}"

    - name: Read ssh key
      ansible.builtin.slurp:
        src: "{{ backup_user_info.home }}/.ssh/backup.pub"
      register: backup_local_ssh_key

    - name: Set authorized key taken from file
      when:
        - borgmatic_initialization_repo is defined and borgmatic_initialization_repo
      ansible.posix.authorized_key:
        # example:
        #   borg_repository: m5vz9gp4@m5vz9gp4.repo.borgbase.com:repo
        #   have three parts: "username"@"FQDN":"path/to/store/backup", specific:
        #     a) user: m5vz9gp4
        #     b) fqdn: m5vz9gp4.repo.borgbase.co
        #     c) dir: repo
        user: "{{ borg_repository | regex_search('(.*)@', '\\1') | first }}" # part a)
        state: present
        key: "{{ backup_local_ssh_key['content'] | b64decode }}"
      delegate_to: "{{ borg_repository | regex_search('@(.*):', '\\1') | first }}" # part b)

    - name: Print key if the borgmatic_initialization_repo is false
      when: borgmatic_initialization_repo is not defined or not borgmatic_initialization_repo
      ansible.builtin.debug:
        msg: "The generated key is: {{ backup_local_ssh_key['content'] | b64decode }}"
...