[develop] Fix an issue where users cannot SSH into LoginNodes with LoginNode-specific keys when different keys are specified for HeadNode and LoginNodes

[hehe7318]

Description of changes

• During Login Node bootstrap before mounting /home:
  • Create a local folder to store the key pair for LoginNodes:
    • /etc/ssh/login_nodes_authorized_keys.d (0755 root:root)
    • /etc/ssh/login_nodes_authorized_keys.d/$DEFAULT_USER/ (0700 $DEFAULT_USER:$DEFAULT_USER)
  • Copy the Login Node key to /etc/ssh/login_nodes_authorized_keys.d/$DEFAULT_USER/authorized_keys (0600 $DEFAULT_USER:$DEFAULT_USER).
  • Append in /etc/ssh/sshd_config:

  AuthorizedKeysFile /etc/ssh/login_nodes_authorized_keys.d/%u/authorized_keys .ssh/authorized_keys
  

Tests

• I am on the manually testing

References

• (3.7.0 – 3.13.0) Cannot SSH into LoginNodes with a Key that differs from the HeadNode’s aws-parallelcluster#6811

Checklist

• Make sure you are pointing to the right branch.
• If you're creating a patch for a branch other than develop add the branch name as prefix in the PR title (e.g. [release-3.6]).
• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

Please review the guidelines for contributing and Pull Request Instructions.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.