Add test-ssh-public-key-auth.sh script

[vxgmichel]

This PR adds a script to test that older OpenSSH client versions can still connect to an XCP-ng server using public key authentication.

Usage

± scripts/test-ssh-public-key-auth.sh 1.2.3.4 7.2_p2-r5 rsa 
Enter root@10.30.36.1 password: 
Pulling Docker image sig9/alpine-openssh-client:7.2_p2-r5...
Generating SSH key pair...
Copying public key to root@1.2.3.4 ...
Verifying SSH connection...
SSH connection successful, cleaning up...
✅ Test passed

Context

Due to the removal of the ssh-rsa signature algorithm in OpenSSH 9.8, older clients (version < 7.2) are no longer able to use public key authentication with ssh-rsa keys. Howerver, newer OpenSSH versions (7.2 and above) should still be able to authenticate using ssh-rsa keys, as well as ed25519 keys. This script can be used to verify this assumption by running a matrix of tests with different OpenSSH client versions and key types against a specified host. In practice, it should be run manually against a test XCP-ng server whenever the OpenSSH RPM package is updated, to ensure that we maintain compatibility with older clients.

Requirements

It requires Docker or Podman to be installed.

Why here?

It was decided during the daily meeting that this was the right place for test scripts that are not integrated in the CI.

Why not integrated in the CI?

Having to depend on Docker/Podman has been deemed to heavy for a script that can be run manually whenever a new OpenSSH RPM package is built. An alternative to consider in the future would be to use a VM image from our lab instead of a docker container.

[LucienLassalle]

My opinion:

• The OpenSSH test suite checks that we can already connect with ED25519 and RSA keys. (Duplicate)
• And if we harden OpenSSH, we'll also need to modify xcp-ng-tests. And I'm afraid this script will rarely/never be used. (Potentially unnecessary work)

[vxgmichel]

Conclusion from daily: we don't want to maintain this, the script can be found in this PR anyway if we need it later.

[vxgmichel]

Quick open/close to update the reference script