Учетные данные учетной записи службы Google P12 - Для чего нужен сертификат?

Question

Мой вопрос: для чего нужен сертификат в учетных данных Google P12?

Я написал следующую программу на Python, которая принимает файл учетных данных учетной записи службы Google в формате P12 (PFX).Эта программа извлекает закрытый ключ и сертификат.

Закрытый ключ используется для подписи JWT при создании токена Google Access (см. Эту статью о создании токенов доступа из учетных данных P12).Я не могу найти применение для сертификата.

Примечание. Этот код также работает с обычными пакетами сертификатов SSL PFX.Центры сертификации помещены в отдельный файл.

'''
Convert a Google P12 (PFX) service account into private key and certificate.
Convert an SSL Certifcate (PFX) into private key, certificate and CAs.
'''

import os
import OpenSSL.crypto

def write_CAs(filename, p12):
    ''' Write the Certificate Authorities, if any, to filename '''

    ca = p12.get_ca_certificates()

    if ca is None:
        return

    if os.path.exists(filename):
        os.remove(filename)

    print('Creating Certificate CA File:', filename)

    with open(filename, 'wb') as f:
        for cert in ca:
            f.write(OpenSSL.crypto.dump_certificate(OpenSSL.crypto.FILETYPE_PEM, cert))

def pfx_to_pem(pfx_path, pfx_password, pkey_path, pem_path, pem_ca_path):
    '''
    Decrypt the P12 (PFX) file and create a private key file and certificate file.

    Input:
        pfx_path    INPUT: This is the Google P12 file or SSL PFX certificate file
        pfx_password    INPUT: Password used to protect P12 (PFX)
        pkey_path   INPUT: File name to write the Private Key to
        pem_path    INPUT: File name to write the Certificate to
        pem_ca_path INPUT: File name to write the Certificate Authorities to
    '''

    print('Opening:', pfx_path)
    with open(pfx_path, 'rb') as f_pfx:
        pfx = f_pfx.read()

    print('Loading P12 (PFX) contents:')
    p12 = OpenSSL.crypto.load_pkcs12(pfx, pfx_password)

    print('Creating Private Key File:', pkey_path)
    with open(pkey_path, 'wb') as f:
        # Write Private Key
        f.write(OpenSSL.crypto.dump_privatekey(OpenSSL.crypto.FILETYPE_PEM, p12.get_privatekey()))

    print('Creating Certificate File:', pem_path)
    with open(pem_path, 'wb') as f:
        # Write Certificate
        f.write(OpenSSL.crypto.dump_certificate(OpenSSL.crypto.FILETYPE_PEM, p12.get_certificate()))

    # Google P12 does not have certifiate authorities but SSL PFX certificates do
    write_CAs(pem_ca_path, p12)

# Start here

pfx_to_pem(
    'compute-engine.p12',   # Google Service Account P12 file
    'notasecret',       # P12 file password
    'compute-engine.key',   # Filename to write private key
    'compute-engine.pem',   # Filename to write certificate
    'compute-engine_ca.pem')# Filename to write CAs if present

Answer 1

Для учетных данных учетной записи службы Google сертификат используется для проверки подписанного JWT.

Подписанный JWT используется для запроса токена доступа с серверов Google OAuth 2.0.

Учетные данные учетной записи службы в формате P12 включают сертификат в виде пакета PKCS # 12.У учетных данных учетной записи службы в формате Json есть сертификат, доступный на веб-сайте Google.

Этот следующий код является примером использования учетных данных Google P12 для создания подписанного JWT, а затем его проверки и отображения содержимого.

'''
This program verifies a Signed JWT created by Google Service Account P12 credentials
First a JWT is signed with the P12 Private Key.
The certificate is extracted from the P12 file and used to verify the signature
'''

import json
import time
import base64
import jwt
import OpenSSL.crypto

# Google Endpoint for creating OAuth 2.0 Access Tokens from Signed-JWT
auth_url = "https://www.googleapis.com/oauth2/v4/token"

# Set how long this token will be valid in seconds
expires_in = 3600   # Expires in 1 hour

#scopes = "https://www.googleapis.com/auth/cloud-platform"
scopes = "https://www.googleapis.com/auth/devstorage.read_only"

# Details on the Google Service Account. The email must match the Google Console.
sa_filename = 'compute-engine.p12'
sa_password = 'notasecret'
sa_email = 'developer-123456@developer.gserviceaccount.com'

# You can control what is verified in the JWT. For example to allow expired JWTs
# set 'verify_exp' to False
options = {
    'verify_signature': True,
    'verify_exp': True,
    'verify_nbf': True,
    'verify_iat': True,
    'verify_aud': True,
    'require_exp': False,
    'require_iat': False,
    'require_nbf': False
}

aud = 'https://www.googleapis.com/oauth2/v4/token'

def load_private_key(p12_path, p12_password):
    ''' Read the private key and return as base64 encoded '''

    # print('Opening:', p12_path)
    with open(p12_path, 'rb') as f:
        data = f.read()

    # print('Loading P12 (PFX) contents:')
    p12 = OpenSSL.crypto.load_pkcs12(data, p12_password)

    # Dump the Private Key in PKCS#1 PEM format
    pkey = OpenSSL.crypto.dump_privatekey(
            OpenSSL.crypto.FILETYPE_PEM,
            p12.get_privatekey())

    # return the private key
    return pkey

def load_public_key(p12_path, p12_password):
    ''' Read the public key and return as base64 encoded '''

    # print('Opening:', p12_path)
    with open(p12_path, 'rb') as f:
        p12_data = f.read()

    # print('Loading P12 (PFX) contents:')
    p12 = OpenSSL.crypto.load_pkcs12(p12_data, p12_password)

    public_key = OpenSSL.crypto.dump_publickey(
                    OpenSSL.crypto.FILETYPE_PEM,
                    p12.get_certificate().get_pubkey())

    # print(public_key)

    return public_key

def create_signed_jwt(p12_path, p12_password, p12_email, scope):
    ''' Create an AccessToken from a service account p12 credentials file '''

    pkey = load_private_key(p12_path, p12_password)

    issued = int(time.time())
    expires = issued + expires_in   # expires_in is in seconds

    # Note: this token expires and cannot be refreshed. The token must be recreated

    # JWT Headers
    additional_headers = {
            "alg": "RS256",
            "typ": "JWT"    # Google uses SHA256withRSA
    }

    # JWT Payload
    payload = {
        "iss": p12_email,   # Issuer claim
        "sub": p12_email,   # Issuer claim
        "aud": auth_url,    # Audience claim
        "iat": issued,      # Issued At claim
        "exp": expires,     # Expire time
        "scope": scope      # Permissions
    }

    # Encode the headers and payload and sign creating a Signed JWT (JWS)
    sig = jwt.encode(payload, pkey, algorithm="RS256", headers=additional_headers)

    # print(sig)

    return sig

def pad(data):
    """ pad base64 string """

    missing_padding = len(data) % 4
    data += '=' * (4 - missing_padding)
    return data

def print_jwt(signed_jwt):
    """ Print a JWT Header and Payload """

    s = signed_jwt.decode('utf-8').split('.')

    print('Header:')
    h = base64.urlsafe_b64decode(pad(s[0])).decode('utf-8')
    print(json.dumps(json.loads(h), indent=4))

    print('Payload:')
    p = base64.urlsafe_b64decode(pad(s[1])).decode('utf-8')
    print(json.dumps(json.loads(p), indent=4))

def verify_signed_jwt(signed_jwt):
    '''
    This function takes a Signed JWT and verifies it using a Google P12 service account.
    '''

    # Get the Public Key
    public_key = load_public_key(sa_filename, sa_password)

    # Verify the Signed JWT
    r = jwt.decode(signed_jwt, public_key, algorithms=["RS256"], audience=aud, options=options)

    print('Decoded JWT:')
    print(json.dumps(r, indent=4))

if __name__ == '__main__':
    s_jwt = create_signed_jwt(sa_filename, sa_password, sa_email, scopes)

    print_jwt(s_jwt)

    verify_signed_jwt(s_jwt)