refactor: add ssh-init in entrypoint again

* feat: latest Alpine 3.23.0
* feat: latest Rsync 3.4.1-r1
* feat: integrate [rsync-docker](https://github.com/JoshPiper/rsync-docker/) 3rd party into this action as 1st party code (no more dependency, better audit, single source of truth)
   - backported:
       - agent-start
       - agent-stop
       - agent-askpass
       - agent-add
       - hosts-add
       - hosts-clear
   - new added: 
       - ssh-init
       - hosts-init
   - improved: 
     - stricter permissions on .ssh/ folder (700) and known_hosts (600)
     - use set -eu in all scipts
* feat: new ``strict_host_keys`` option to enable support for strict host key verification. Default: false (to keep backward compatibility)
* feat: new ``debug`` option to see the commands executed (-x) by this action
* feat: this action is now scanned for vulnerabilities by Snyk
* feat; this action is now scanned by CodeQL for Q/A
* feat: this action now performs CI tasks such as Validation, Linting and Unit Tests
* fix: various shell syntax for robustness
* fix: use printf and redirect output to non-stdout instead of echo in sensitive code locations
* refactor: use $HOME instead of tilde ~ for robustness
* feat: cross-platform support
* chore: Deprecate 7.0.2
* chore: EOL 7.0.0 & 7.0.1

Dockerfile

@@ -5,7 +5,7 @@ RUN apk update && apk add --no-cache --upgrade rsync openssh openssl busybox
 RUN rm -rf /var/cache/apk/*
 
 COPY docker-rsync/* /bin/
-RUN chmod +x /bin/agent-*
+RUN chmod +x /bin/agent-* /bin/ssh-* /bin/hosts-*
 
 FROM base AS build
 

docker-rsync/README.md

@@ -0,0 +1,40 @@
+# Scripts
+
+Shell-scripts to help with managing SSH agents and known hosts files.
+
+### SSH Management
+
+#### ssh-init
+This command create the ``$HOME/.ssh`` folder with default permissions ``700``.
+
+### SSH-Agent Management
+
+#### agent-start
+This command starts the SSH agent, if it isn't already started (SSH_AGENT_PID set or ssh agent ID file found).
+It takes one optional argument, for the name of the agent to be started. Defaults to "default".
+This program needs to be source'd to work correctly.
+`source agent-start "default"`
+
+#### agent-stop
+This command stops the SSH agent, if it is started (SSH_AGENT_PID set or ssh agent ID file found).
+It takes one optional argument, for the name of the agent to be stopped. Defaults to "default".
+`agent-stop "my-agent-name"`
+
+#### agent-add
+This command adds a key to the currently running SSH agent. The key is taken from stdin, and the agent used is that in SSH_AGENT_PID.
+
+#### agent-askpass
+This command is called by ssh-add when the [SSH_ASKPASS](https://man.openbsd.org/ssh-add.1#ENVIRONMENT) variable is set active. The command returns the SSH_PASS to [ssh-askpass(1)](https://man.openbsd.org/ssh-askpass.1).
+
+This command is ignored by ssh-add if the key does not require a passphrase.
+
+### known_hosts management
+
+#### hosts-init
+This command creates the known_hosts file (``$HOME/.ssh/known_hosts``) with default permission ``600``.
+
+#### hosts-add
+This command adds an entry to the known hosts file, and ensures its permissions are correct. It takes one argument, which is the new key to add.
+
+#### hosts-clear
+This command truncates the known_hosts file.

entrypoint.sh

@@ -17,7 +17,7 @@ source hosts-init
 
 # Start the SSH agent and load key.
 source agent-start "$GITHUB_ACTION"
-printf '%s' "$INPUT_REMOTE_KEY" | SSH_PASS="${INPUT_REMOTE_KEY_PASS}" agent-add >/dev/null 2>&1
+echo "$INPUT_REMOTE_KEY" | SSH_PASS="$INPUT_REMOTE_KEY_PASS" agent-add
 
 # Variables.
 LEGACY_RSA_HOSTKEYS=""