User's ssh-keys are a list that is now being iterated over

defaults/main.yml

@@ -1,7 +1,9 @@
 ---
 basic_users:
   - name: "madonius"
-    ssh_auth_key: ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIB3HexVmU/vTVFUFk2AAB1h3mOOrfFPt1Gq2cBldaYnn madonius@iapeptus
+    ssh_auth_key:
+      - ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIB3HexVmU/vTVFUFk2AAB1h3mOOrfFPt1Gq2cBldaYnn madonius@iapeptus
+      - ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAICjSv7S3EMXmmpuHs7AtrK/D3x5zMiRlcddKgrAoqMTt ekampitakis@aretousa
     uid: 1337
     shell: /bin/zsh
     comment: ""

tasks/users.yml

@@ -12,5 +12,6 @@
 - name: Copy local ssh key to authorized keys file
   authorized_key:
     user: "{{ os_user.name }}"
-    key: "{{ os_user.ssh_auth_key }}"
+    key: "{{ item }}"
+  loop: "{{ os_user.ssh_auth_keys }}"
   become: true