Chris Farhood
f425b5191e
The previous implementation had a stdin conflict -- it passed the PEM key on stdin but also needed to pass the unsigned data on stdin. Now that we take a file path, openssl reads the key from the file and gets the data to sign from stdin. Also removed the dead-code tempfile fallback and unused hashlib import.
85 lines
2.5 KiB
Python
Executable File
85 lines
2.5 KiB
Python
Executable File
#!/usr/bin/env python3
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"""Generate a JWT for GitHub App authentication.
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Reads from environment variables:
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GITHUB_APP_ID - The GitHub App's numeric ID
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GITHUB_APP_PEM_FILE - Path to the PEM-encoded private key file
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Prints the signed JWT to stdout.
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"""
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import json
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import os
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import sys
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import time
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import base64
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try:
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from cryptography.hazmat.primitives import hashes, serialization
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from cryptography.hazmat.primitives.asymmetric import padding
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USE_CRYPTOGRAPHY = True
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except ImportError:
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import subprocess
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USE_CRYPTOGRAPHY = False
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def b64url(data: bytes) -> str:
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return base64.urlsafe_b64encode(data).rstrip(b"=").decode("ascii")
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def sign_with_cryptography(unsigned: str, pem_contents: str) -> str:
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"""Sign using the cryptography library. Handles both PKCS#1 and PKCS#8 PEM formats."""
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private_key = serialization.load_pem_private_key(pem_contents.encode(), password=None)
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signature = private_key.sign(unsigned.encode(), padding.PKCS1v15(), hashes.SHA256())
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return b64url(signature)
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def sign_with_openssl(unsigned: str, pem_file: str) -> str:
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"""Sign using the openssl CLI. Reads the key from the file path directly."""
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result = subprocess.run(
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["openssl", "dgst", "-sha256", "-sign", pem_file, "-binary"],
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input=unsigned.encode(),
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capture_output=True,
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)
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if result.returncode != 0:
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print(f"error: openssl signing failed: {result.stderr.decode()}", file=sys.stderr)
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sys.exit(1)
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return b64url(result.stdout)
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def main():
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app_id = os.environ.get("GITHUB_APP_ID")
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pem_file = os.environ.get("GITHUB_APP_PEM_FILE")
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if not app_id:
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print("error: GITHUB_APP_ID is not set", file=sys.stderr)
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sys.exit(1)
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if not pem_file:
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print("error: GITHUB_APP_PEM_FILE is not set", file=sys.stderr)
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sys.exit(1)
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if not os.path.isfile(pem_file):
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print(f"error: PEM file not found: {pem_file}", file=sys.stderr)
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sys.exit(1)
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now = int(time.time())
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header = b64url(json.dumps({"alg": "RS256", "typ": "JWT"}).encode())
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payload = b64url(
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json.dumps({"iat": now - 60, "exp": now + 600, "iss": app_id}).encode()
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)
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unsigned = f"{header}.{payload}"
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if USE_CRYPTOGRAPHY:
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with open(pem_file, "r") as f:
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pem_contents = f.read()
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signature = sign_with_cryptography(unsigned, pem_contents)
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else:
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signature = sign_with_openssl(unsigned, pem_file)
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print(f"{unsigned}.{signature}")
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if __name__ == "__main__":
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main()
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