refactor: replace github-app-token docs with executable script

Move token generation logic from inline SKILL.md code blocks into a
single scripts/generate-token.sh that agents can invoke directly.
Adds env var validation, error handling, and gh CLI auth in one step.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

github-app-token/SKILL.md

@@ -5,84 +5,22 @@ description: Generate a GitHub installation access token from a GitHub App PEM k
 
 # GitHub App Token Skill
 
-Generate a short-lived GitHub installation access token from a GitHub App's credentials and use it to authenticate the `gh` CLI.
+Generate a short-lived GitHub App installation token and authenticate `gh`.
 
-## Prerequisites
+## Required Environment Variables
-
-The following environment variables MUST be set before invoking this skill:
 
 | Variable | Description |
 |---|---|
-| `GITHUB_APP_ID` | The numeric App ID from the GitHub App settings page |
+| `GITHUB_APP_ID` | Numeric App ID from GitHub App settings |
-| `GITHUB_APP_INSTALLATION_ID` | The numeric Installation ID for the target org/user |
+| `GITHUB_APP_INSTALLATION_ID` | Numeric Installation ID for the target org/user |
-| `GITHUB_APP_PEM_FILE` | Absolute path to the GitHub App's PEM private key file |
+| `GITHUB_APP_PEM_FILE` | Absolute path to the App's PEM private key file |
 
-If any variable is missing, stop and tell the user which ones are required.
+## Usage
-
-Requires `openssl`, `curl`, and `jq`.
-
-## Generate a Token
-
-Build a JWT signed with the App's private key, then exchange it for an installation access token and write it to a file:
 
 ```bash
-# Base64url helper
+bash github-app-token/scripts/generate-token.sh
-b64enc() { openssl enc -base64 -A | tr '+/' '-_' | tr -d '='; }
-
-# Build JWT (valid 10 minutes)
-NOW=$(date +%s)
-HEADER=$(printf '{"alg":"RS256","typ":"JWT"}' | jq -r -c .)
-PAYLOAD=$(printf '{"iat":%s,"exp":%s,"iss":"%s"}' "$NOW" "$((NOW + 600))" "$GITHUB_APP_ID" | jq -r -c .)
-SIGNED=$(printf '%s' "$HEADER" | b64enc).$(printf '%s' "$PAYLOAD" | b64enc)
-SIG=$(printf '%s' "$SIGNED" | openssl dgst -binary -sha256 -sign "$GITHUB_APP_PEM_FILE" | b64enc)
-JWT="${SIGNED}.${SIG}"
-
-# Token file — unique per agent to avoid env-var collisions
-GH_TOKEN_FILE="${AGENT_HOME:+${AGENT_HOME}/.gh-token}"
-GH_TOKEN_FILE="${GH_TOKEN_FILE:-$(mktemp)}"
-
-# Exchange JWT for installation token and write to file
-curl -s -X POST \
-  -H "Authorization: Bearer ${JWT}" \
-  -H "Accept: application/vnd.github+json" \
-  -H "X-GitHub-Api-Version: 2022-11-28" \
-  "https://api.github.com/app/installations/${GITHUB_APP_INSTALLATION_ID}/access_tokens" \
-  | jq -r '.token' > "$GH_TOKEN_FILE"
-
-chmod 600 "$GH_TOKEN_FILE"
 ```
 
-The token file path defaults to `$AGENT_HOME/.gh-token` (unique per agent) or a temporary file when `AGENT_HOME` is not set. This avoids env-var collisions when multiple agents generate tokens concurrently.
+The script validates env vars, generates a JWT, exchanges it for an installation token, writes the token to `$AGENT_HOME/.gh-token`, and runs `gh auth login`. On success it prints a confirmation line. On failure it exits non-zero with a descriptive error.
 
-## Authenticate the gh CLI
+Requires `openssl`, `curl`, `jq`, and `gh`.
-
-Read the token from the file and log in:
-
-```bash
-gh auth login --with-token < "$GH_TOKEN_FILE"
-```
-
-To use `GH_TOKEN` in a single command without polluting the environment:
-
-```bash
-GH_TOKEN=$(cat "$GH_TOKEN_FILE") gh api user
-```
-
-## Cleanup
-
-The installation access token expires after 1 hour. To revoke it early and remove the token file:
-
-```bash
-curl -s -X DELETE \
-  -H "Authorization: Bearer $(cat "$GH_TOKEN_FILE")" \
-  -H "Accept: application/vnd.github+json" \
-  "https://api.github.com/installation/token"
-rm -f "$GH_TOKEN_FILE"
-```
-
-## Security Notes
-
-- Never log or echo the PEM key or installation token to stdout in production.
-- The installation token is valid for 1 hour from generation.
-- Store the PEM file with restrictive permissions (`chmod 600`) and never check it into git.
-- The token file is written with mode `600` and should be cleaned up after use.

github-app-token/scripts/generate-token.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+die() { echo "ERROR: $*" >&2; exit 1; }
+
+# --- Validate required env vars ---
+[[ -z "${GITHUB_APP_ID:-}" ]]              && die "GITHUB_APP_ID is not set"
+[[ -z "${GITHUB_APP_INSTALLATION_ID:-}" ]] && die "GITHUB_APP_INSTALLATION_ID is not set"
+[[ -z "${GITHUB_APP_PEM_FILE:-}" ]]        && die "GITHUB_APP_PEM_FILE is not set"
+[[ ! -f "$GITHUB_APP_PEM_FILE" ]]          && die "PEM file not found: $GITHUB_APP_PEM_FILE"
+
+for cmd in openssl curl jq gh; do
+  command -v "$cmd" >/dev/null 2>&1 || die "Required command not found: $cmd"
+done
+
+# --- Build JWT (valid 10 minutes) ---
+b64url() { openssl enc -base64 -A | tr '+/' '-_' | tr -d '='; }
+
+NOW=$(date +%s)
+HEADER=$(printf '{"alg":"RS256","typ":"JWT"}' | b64url)
+PAYLOAD=$(printf '{"iat":%s,"exp":%s,"iss":"%s"}' "$NOW" "$((NOW + 600))" "$GITHUB_APP_ID" | b64url)
+SIGNED="${HEADER}.${PAYLOAD}"
+SIG=$(printf '%s' "$SIGNED" | openssl dgst -binary -sha256 -sign "$GITHUB_APP_PEM_FILE" | b64url)
+JWT="${SIGNED}.${SIG}"
+
+# --- Exchange JWT for installation access token ---
+RESPONSE=$(curl -sf -X POST \
+  -H "Authorization: Bearer ${JWT}" \
+  -H "Accept: application/vnd.github+json" \
+  -H "X-GitHub-Api-Version: 2022-11-28" \
+  "https://api.github.com/app/installations/${GITHUB_APP_INSTALLATION_ID}/access_tokens") \
+  || die "GitHub API request failed — check App ID, Installation ID, and PEM key"
+
+TOKEN=$(echo "$RESPONSE" | jq -r '.token // empty')
+[[ -z "$TOKEN" ]] && die "No token in GitHub response: $RESPONSE"
+
+# --- Write token to file ---
+GH_TOKEN_FILE="${AGENT_HOME:+${AGENT_HOME}/.gh-token}"
+GH_TOKEN_FILE="${GH_TOKEN_FILE:-$(mktemp)}"
+
+printf '%s' "$TOKEN" > "$GH_TOKEN_FILE"
+chmod 600 "$GH_TOKEN_FILE"
+
+# --- Authenticate gh CLI ---
+gh auth login --with-token < "$GH_TOKEN_FILE"
+
+echo "Authenticated. Token written to $GH_TOKEN_FILE (expires in 1 hour)."