45 lines
1.4 KiB
Plaintext
45 lines
1.4 KiB
Plaintext
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#!/usr/bin/env bash
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# Initialize tunnel-only SSH auth for BackTunnel (Option A)
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# Usage: backtunnel-auth-setup [-p PORT] user@localhost
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set -euo pipefail
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PORT=2222
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while [[ $# -gt 0 ]]; do
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case "$1" in
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-p|--port) PORT="$2"; shift 2;;
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-h|--help)
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echo "Usage: backtunnel-auth-setup [-p PORT] user@localhost"
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exit 0;;
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*) break;;
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esac
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done
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DEST="${1:-}"
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[[ -n "$DEST" ]] || { echo "Missing destination (e.g., user@localhost)."; exit 1; }
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KEY="$HOME/.ssh/id_ed25519_backtunnel"
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PUB="$KEY.pub"
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# 1) Create a dedicated key if missing
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if [[ ! -f "$KEY" ]]; then
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echo "Generating dedicated key at $KEY ..."
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ssh-keygen -t ed25519 -f "$KEY" -N "" -C "backtunnel"
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fi
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# 2) Append restricted key only (idempotent): tunnel-only + SFTP-only
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echo "Installing restricted key (tunnel-only, SFTP-only) via port $PORT ..."
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RESTRICTED_LINE="$(printf 'from="127.0.0.1",command="internal-sftp",restrict '; cat "$PUB")"
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ssh -p "$PORT" "$DEST" bash -lc '
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set -euo pipefail
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umask 077
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mkdir -p ~/.ssh
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touch ~/.ssh/authorized_keys
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chmod 600 ~/.ssh/authorized_keys
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# Only append if not already present
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if ! grep -Fqx -- "$RESTRICTED_LINE" ~/.ssh/authorized_keys 2>/dev/null; then
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printf "%s\n" "$RESTRICTED_LINE" >> ~/.ssh/authorized_keys
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fi
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' _ RESTRICTED_LINE="$RESTRICTED_LINE"
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echo "Done. This key will only work via the reverse tunnel (127.0.0.1) and only for SFTP."
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