Configure Agent Pr Attestation

Configure Agent PR Attestation

Sets up a PostToolUse hook that signs and uploads an in-toto attestation to the Harness Evidence Vault every time an AI coding agent creates a PR/MR.

Instructions

Follow these steps in exact order. Do NOT skip steps or reorder them.

Step 1: Check Prerequisites

Run these checks and report what's missing. Do not proceed until all are installed.

command -v harness-scs
command -v jq
command -v git
command -v cosign

If harness-scs is missing, tell the user:

task compile-harness-scs && sudo mv harness-scs /usr/local/bin/

Step 2: Ask for SCM

Ask the user which tool they use to create PRs/MRs. Use AskUserQuestion.

Options:

If user picks GitLab, Bitbucket, Gitea, or Custom — also ask if self-hosted. If self-hosted, ask for hostname and replace the generic [^ ]+ host in the url_pattern with their specific escaped hostname.

If user picks "Other / custom":

1. Ask for the exact command they run.
2. Ask for an example PR URL their tool prints.
3. Derive command_filter and url_pattern, show to user, confirm.

Step 3: Set up Harness Identity (auth.json)

Check if ~/.harness/auth.json already exists:

test -r ~/.harness/auth.json && jq -e '.token and .account_id' ~/.harness/auth.json >/dev/null 2>&1

If auth.json exists and is valid: Tell the user "Found existing ~/.harness/auth.json" and move to Step 4.

If auth.json does NOT exist: Ask the user for these values:

• API key (PAT, format: pat.<account>.<random>.<random>)
• API URL (default: https://app.harness.io)
• Account ID (can be auto-derived from PAT if empty)
• Org ID
• Project ID

Then create ~/.harness/auth.json:

mkdir -p ~/.harness
cat > ~/.harness/auth.json << 'EOF'
{
  "token": "<API key>",
  "base_url": "<API URL>",
  "account_id": "<Account ID>",
  "org_id": "<Org ID>",
  "project_id": "<Project ID>"
}
EOF
chmod 600 ~/.harness/auth.json

Step 4: Set up Cosign Key and scs.env

Ask the user via AskUserQuestion:

Cosign signing key:
  - I already have one         → ask for absolute path
  - Generate a new one for me  → generate in ~/.harness/

If generating:

mkdir -p ~/.harness
cd ~/.harness && COSIGN_PASSWORD="" cosign generate-key-pair
chmod 600 ~/.harness/cosign.key

Set key_path="$HOME/.harness/cosign.key".

If existing key: Ask for the absolute path. Validate it's readable. Warn if password-protected — they'll need to set COSIGN_PASSWORD for unattended runs.

Then write ~/.harness/scs.env (do NOT ask where to put it — always this path):

cat > ~/.harness/scs.env << 'EOF'
export HARNESS_SIGNER_KEY_PATH="<key_path>"
export COSIGN_PASSWORD=""
EOF

scs.env contains ONLY cosign signer variables. Never put Harness identity here.

Step 5: Generate the Hook Script

Write to <project>/.claude/hooks/agent-pr-attestation.sh, substituting:

• {{COMMAND_FILTER}} ← from Step 2
• {{URL_REGEX}} ← from Step 2
• {{KEY_PATH}} ← from Step 4

Then chmod +x the script.

#!/bin/bash
# Generated by configure-agent-pr-attestation skill.
# Captures a signed in-toto attestation when an AI agent creates a PR.
#
# To reconfigure: re-run /configure-agent-pr-attestation in your agent.

set -uo pipefail

[ -f ~/.harness/scs.env ] && source ~/.harness/scs.env

COMMAND_FILTER='{{COMMAND_FILTER}}'
URL_REGEX='{{URL_REGEX}}'

INPUT=$(cat)
COMMAND=$(echo "$INPUT" | jq -r '.tool_input.command // empty')

if ! echo "$COMMAND" | grep -qE "$COMMAND_FILTER"; then
  exit 0
fi

TRANSCRIPT_PATH=$(echo "$INPUT" | jq -r '.transcript_path')
TOOL_STDOUT=$(echo "$INPUT" | jq -r '.tool_response.stdout // empty')
TOOL_STDERR=$(echo "$INPUT" | jq -r '.tool_response.stderr // empty')
CWD=$(echo "$INPUT" | jq -r '.cwd')

PR_URL=$(printf '%s\n%s\n' "$TOOL_STDOUT" "$TOOL_STDERR" | grep -oE "$URL_REGEX" | head -1)
COMMIT_SHA=$(cd "$CWD" && git rev-parse HEAD 2>/dev/null)

if [ -z "$PR_URL" ] || [ -z "$COMMIT_SHA" ]; then
  exit 0
fi

PR_NUMBER=$(echo "$PR_URL" | grep -oE '[0-9]+$')
EXECUTION_ID="harness-pr-attestor-${PR_NUMBER:-$(date +%s)}"

PASSPHRASE_FILE=$(mktemp -t harness-scs-passphrase.XXXXXX)
trap 'rm -f "$PASSPHRASE_FILE"' EXIT
chmod 600 "$PASSPHRASE_FILE"
printf '%s' "${COSIGN_PASSWORD:-}" >"$PASSPHRASE_FILE"

harness-scs attestation run \
  --step "agent-pull-request" \
  --attestations claudecode \
  --attestor-claudecode-session-file "$TRANSCRIPT_PATH" \
  --attestor-claudecode-include-thinking \
  --attestor-claudecode-commit-sha "$COMMIT_SHA" \
  --attestor-claudecode-pr-url "$PR_URL" \
  --signer-file-key-path "${HARNESS_SIGNER_KEY_PATH:-{{KEY_PATH}}}" \
  --signer-file-key-passphrase-path "$PASSPHRASE_FILE" \
  --enable-attestation-upload \
  --execution-id "$EXECUTION_ID" \
  >/dev/null 2>&1

exit 0

Step 6: Patch .claude/settings.json

Register the hook with Claude Code. Use project-scoped settings by default.

Read existing .claude/settings.json (create {} if absent), then merge in:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "$CLAUDE_PROJECT_DIR/.claude/hooks/agent-pr-attestation.sh"
          }
        ]
      }
    ]
  }
}

Make this idempotent — don't duplicate if already present.

After patching, confirm setup is complete and tell the user to verify by creating a test PR in a new session.

Troubleshooting

Reconfiguration

If the user re-runs the skill, detect existing files and offer:

• "An existing hook was found at <path>. Replace it?"
• "Existing cosign key at <path> — keep it or regenerate?"
• "Found ~/.harness/auth.json — keep or update?"

Never silently overwrite.

Limitations

Only cosign file keys are supported for signing. If the user asks about keyless signing (Fulcio), KMS signers, or non-Claude-Code agent runtimes, tell them these are not yet available.