如何使用 REST API 从服务帐户凭据创建访问令牌？

Question

我在 Google Cloud Platform 中创建了一个服务帐户并下载了 JSON 格式的私钥。我正在尝试通过 REST API 创建一个计算资源。出于身份验证的目的，我需要一个 AccessToken，它需要设置为创建计算资源 REST API 的标头。是否有 REST API 从私钥获取访问令牌（不使用 SDK 或 Google 客户端）？

Answer 1

有一种更简单的方法可以使用 Google 库从服务帐户生成令牌

from google.auth.transport import requests
from google.oauth2 import service_account

CREDENTIAL_SCOPES = ["https://www.googleapis.com/auth/cloud-platform"]
CREDENTIALS_KEY_PATH = '/PATH/TO/SERVICE_ACCOUNT.json'

def get_service_account_token():
  credentials = service_account.Credentials.from_service_account_file(
          CREDENTIALS_KEY_PATH, scopes=CREDENTIAL_SCOPES)
  credentials.refresh(requests.Request())
  return credentials.token

或者如果您想使用默认身份验证

import google
from google.auth.transport import requests

CREDENTIAL_SCOPES = ["https://www.googleapis.com/auth/cloud-platform"] 

def get_default_token():
  credentials, project_id = google.auth.default(scopes=CREDENTIAL_SCOPES)
  credentials.refresh(requests.Request())
  return credentials.token

credentials对象创建时，token为空，但刷新credentials后，包含了可以作为API请求头的访问token

Answer 2

以下示例向您展示了在不使用 Python 中的 SDK 的情况下调用 Google Cloud API 的几个重要步骤。类似的代码几乎适用于任何语言（c#、java、php、nodejs）。

使用您的服务帐户 Json 文件的文件名、您的 Google 区域和您的项目 ID 更改源代码。

此示例将列出指定项目的一个区域中的实例。通过这个示例，您将了解调用 API 以创建 GCE 实例的框架。

此代码将向您展示如何：

1. 如何从 Json 文件加载服务帐户凭据。
2. 如何提取用于签署请求的私钥。
3. 如何为 Google Oauth 2.0 创建 JWT（Json Web 令牌）。
4. 如何设置 Google 范围（权限）。
5. 如何签署 JWT 以创建 Signed-JWT (JWS)。
6. 如何将 Signed-JWT 交换为 Google OAuth 2.0 访问令牌。
7. 如何设置过期时间。此程序默认为 3600 秒（1 小时）。
8. 如何调用 Google API 并设置授权标头。
9. 如何处理返回的Json结果并显示每个实例的名称。

Python 3.x 中的示例程序：

'''
This program lists lists the Google Compute Engine Instances in one zone
'''
# Author: John Hanley
# https://www.jhanley.com

import time
import json
import jwt
import requests
import httplib2

# Project ID for this request.
project = 'development-123456'

# The name of the zone for this request.
zone = 'us-west1-a'

# Service Account Credentials, Json format
json_filename = 'service-account.json'

# Permissions to request for Access Token
scopes = "https://www.googleapis.com/auth/cloud-platform"

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

def load_json_credentials(filename):
    ''' Load the Google Service Account Credentials from Json file '''

    with open(filename, 'r') as f:
        data = f.read()

    return json.loads(data)

def load_private_key(json_cred):
    ''' Return the private key from the json credentials '''

    return json_cred['private_key']

def create_signed_jwt(pkey, pkey_id, email, scope):
    ''' Create a Signed JWT from a service account Json credentials file
    This Signed JWT will later be exchanged for an Access Token '''

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

    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 = {
            'kid': pkey_id,
            "alg": "RS256",
            "typ": "JWT"    # Google uses SHA256withRSA
    }

    # JWT Payload
    payload = {
        "iss": email,       # Issuer claim
        "sub": 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)

    return sig

def exchangeJwtForAccessToken(signed_jwt):
    '''
    This function takes a Signed JWT and exchanges it for a Google OAuth Access Token
    '''

    auth_url = "https://www.googleapis.com/oauth2/v4/token"

    params = {
        "grant_type": "urn:ietf:params:oauth:grant-type:jwt-bearer",
        "assertion": signed_jwt
    }

    r = requests.post(auth_url, data=params)

    if r.ok:
        return(r.json()['access_token'], '')

    return None, r.text

def gce_list_instances(accessToken):
    '''
    This functions lists the Google Compute Engine Instances in one zone
    '''

    # Endpoint that we will call
    url = "https://www.googleapis.com/compute/v1/projects/" + project + "/zones/" + zone + "/instances"

    # One of the headers is "Authorization: Bearer $TOKEN"
    headers = {
        "Host": "www.googleapis.com",
        "Authorization": "Bearer " + accessToken,
        "Content-Type": "application/json"
    }

    h = httplib2.Http()

    resp, content = h.request(uri=url, method="GET", headers=headers)

    status = int(resp.status)

    if status < 200 or status >= 300:
        print('Error: HTTP Request failed')
        return

    j = json.loads(content.decode('utf-8').replace('\n', ''))

    print('Compute instances in zone', zone)
    print('------------------------------------------------------------')
    for item in j['items']:
        print(item['name'])

if __name__ == '__main__':
    cred = load_json_credentials(json_filename)

    private_key = load_private_key(cred)

    s_jwt = create_signed_jwt(
            private_key,
            cred['private_key_id'],
            cred['client_email'],
            scopes)

    token, err = exchangeJwtForAccessToken(s_jwt)

    if token is None:
        print('Error:', err)
        exit(1)

    gce_list_instances(token)

有关更多信息，请访问我的博客。我写这样的文章并发布源代码以帮助其他人了解如何为云编写软件。

www.jhanley.com

Answer 3

使用 JAVA 的相同解决方案

import com.google.auth.oauth2.GoogleCredentials;
import java.io.FileInputStream;
import java.io.IOException;

public class GoogleHelper {
    public static String getAccessToken() throws IOException {
        return GoogleCredentials
                .fromStream(new FileInputStream("/PATH/TO/SERVICE_ACCOUNT.json"))
                .createScoped("https://www.googleapis.com/auth/cloud-platform")
                .refreshAccessToken()
                .getTokenValue();
    }
}