How to upload ssh public key to as authorized_key using Ansible

Step 1: Create hosts inventory file

You need to tell Ansible which hosts you are going to use:
$ cat my_ssh_hosts
Sample outputs:

server1.cyberciti.biz
server2.cyberciti.biz
server3.cyberciti.biz

Step 2: Create playbook

Create a file called upload_ssh_keys.yml as follows:

---
- hosts: all
  remote_user: vivek
  tasks:
          # upload ssh key                
          - authorized_key:
                  user: vivek
                  state: present
                  manage_dir: yes
                  key: "{{ lookup('file', '/path/to/your/www_id_rsa.pub') }}"
# vim:ft=ansible:

The above will place public key file (/path/to/your/www_id_rsa.pub) to all server listed my_ssh_hosts file. Make sure you setup ssh keys for root account.

Step 3: Run playbook

The syntax is:
$ ansible-playbook -i my_ssh_hosts upload_ssh_keys.yml

Another example

In this example, a new user named vivek is created. Next ssh key added for user vivek and ssh server configured to drop password based login using ssh-setup.j2 template.

File: ssh-setup.yml

---
- hosts: cluster
  tasks:
          # create users for us
          # note user vivek added to sudo group 
          # on many system you may need to use wheel 
          # user in sudo or wheel group can sudo
          - user:
                  name: vivek
                  comment: "Vivek Gite"
                  shell: /bin/bash
                  groups: sudo
                  append: yes
                  generate_ssh_key: yes
                  ## run command 'mkpasswd --method=sha-512' to create your own encrypted password ##
                  password: $6$gF1EHgeUSSwDT3$xgw22QBdZfNe3OUjJkwXZOlEsL645TpacwiYwTwlUyah03.Zh1aUTTfh7iC7Uu5WfmHBkv5fxdbJ2OkzMAPkm/
                  ssh_key_type: ed25519
          # upload ssh key                
          - authorized_key:
                  user: vivek
                  state: present
                  manage_dir: yes
                  key: "{{ lookup('file', '/home/vivek/.ssh/id_ed25519.pub') }}"
          # configure ssh server
          - template:
                  src: ssh-setup.j2
                  dest: /etc/ssh/sshd_config
                  owner: root
                  mode: '0600'
                  validate: /usr/sbin/sshd -t -f %s
                  backup: yes
          # restart sshd
          - service:
                  name: sshd
                  state: restarted

File: ssh-setup.j2

The following will disable root login and password login. Only user named vivek may be login over ssh using public key (you need to issue sudo -i command to gain root shell):

Port 22
Protocol 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key
UsePrivilegeSeparation sandbox
KeyRegenerationInterval 3600
ServerKeyBits 1024
SyslogFacility AUTH
LogLevel INFO
LoginGraceTime 120
PermitRootLogin {{ sshd_permitroot_login }}
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
LogLevel VERBOSE
IgnoreRhosts yes
RhostsRSAAuthentication no
HostbasedAuthentication no
PermitEmptyPasswords no
ChallengeResponseAuthentication no
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
UsePAM {{ sshd_use_pam }}
PasswordAuthentication {{ sshd_password_authentication }}
ChallengeResponseAuthentication {{ sshd_challenge_response_authentication }}
{% for nip in ansible_all_ipv4_addresses  %}
ListenAddress {{ nip }}
{% endfor %}

File: my-inventory.hosts

[all:vars]
ansible_user=root
ansible_port=22
 
[cluster:vars]
sshd_use_pam=no
sshd_password_authentication=no
sshd_challenge_response_authentication=no
sshd_permitroot_login=no
 
[cluster]
server1.cyberciti.biz
server2.cyberciti.biz
server3.cyberciti.biz

You run it as follows:
$ ansible-playbook -i my-inventory.hosts ssh-setup.yml
You can also use loops as follows to upload file for each user:

- hosts: all
  user: root
# ....
  
my_ssh_users:
  - name: vivek
    key: "{{ lookup('file', 'vivek.pub') }}"
  - name: tom
    key: "{{ lookup('file', 'tom.pub') }}"
  - name: wendy
    key: "{{ lookup('file', 'wendy.pub') }}"
  - name: jerry
    key: "{{ lookup('file', 'jerry.pub') }}"
# ...
- name: Add ssh pub keys
  authorized_key: user={{ item.name }} key="{{ item.key }}"
  with_items: my_ssh_users

See authorized_key module doc for more info.