$USER_AT_HOST="your-user-name-on-host@hostname"
$PUBKEYPATH="$HOME\.ssh\id_rsa.pub"

$pubKey=(Get-Content "$PUBKEYPATH" | Out-String); ssh "$USER_AT_HOST" "mkdir -p ~/.ssh && chmod 700 ~/.ssh && echo '${pubKey}' >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"