action.yml

name: Install SSH key
description: Stores a private SSH key on the GitHub Actions runner and adds it to the SSH agent.
author: Steffen Diswal

inputs:
  key-name:
    description: The name of the file in the `.ssh` directory that stores the value of `__private-key__`.
    required: false
    default: "id_ed25519"
  #
  known-hosts:
    description: A newline-separated list of trusted remote host keys to be stored in `.ssh/known_hosts`.
    required: true
  #
  __private-key__:
    description: The private SSH key to be stored in `.ssh/<key-name>` and added to the SSH agent on the GitHub Actions runner.
    required: true

runs:
  using: composite
  steps:
    # language=sh
    - run: |
        if [[ ! "$KEY_NAME" =~ ^[0-9A-Za-z_.-]+$ ]]; then
          echo 'Input parameter `key-name` must be non-empty and contain letters, numbers, dashes, underscores, and periods only.'
          exit 2
        elif [[ -z "$KNOWN_HOSTS" ]]; then
          echo 'Input parameter `known-hosts` must be non-empty.'
          exit 2
        elif [[ -z "$PRIVATE_KEY" ]]; then
          echo 'Input parameter `__private-key__` must be non-empty.'
          exit 2
        fi

        mkdir "$HOME/.ssh"
        echo "$KNOWN_HOSTS" > "$HOME/.ssh/known_hosts"
        chmod 644 "$HOME/.ssh/known_hosts"

        echo "$PRIVATE_KEY" > "$HOME/.ssh/$KEY_NAME"
        chmod 600 "$HOME/.ssh/$KEY_NAME"

        eval "$(ssh-agent -s)"
        echo "SSH_AGENT_PID=$SSH_AGENT_PID" >> "$GITHUB_ENV"
        echo "SSH_AUTH_SOCK=$SSH_AUTH_SOCK" >> "$GITHUB_ENV"

        ssh-add "$HOME/.ssh/$KEY_NAME"
      env:
        KEY_NAME: ${{ inputs.key-name }}
        KNOWN_HOSTS: ${{ inputs.known-hosts }}
        PRIVATE_KEY: ${{ inputs.__private-key__ }}
      shell: bash