使用 Gmail API 管理 S/MIME 憑證

本文說明如何透過 Gmail API 使用 S/MIME 電子郵件憑證。

透過 Gmail API，您可以透過程式輔助方式，管理 Google Workspace 網域中使用者使用的 S/MIME 電子郵件憑證。

管理員必須為網域啟用代管式 S/MIME，憑證才能正常運作。

S/MIME 標準提供 MIME 資料的公開金鑰加密和簽署規格。為使用者帳戶設定 S/MIME 憑證後，Gmail 會以以下方式使用這些憑證：

  • 使用使用者憑證和私密金鑰簽署外寄郵件。

  • 使用使用者私密金鑰解密收到的郵件。

  • 使用收件者憑證和公開金鑰加密外寄郵件。

  • 使用寄件者憑證和公開金鑰驗證來信。

您可以產生個別的 S/MIME 憑證，然後使用 Gmail API 上傳。每個 S/MIME 憑證都適用於使用者電子郵件帳戶的特定別名。別名包括主要電子郵件地址和自訂「以這個地址傳送郵件」地址。API 會將單一 S/MIME 憑證標示為每個別名的預設憑證。

如要進一步瞭解別名，請參閱「使用 Gmail API 管理別名和簽名」。

授權 API 存取權

如要授權存取 Gmail API，請使用下列其中一種方法：

  1. 使用服務帳戶，並委派全網域授權。如要瞭解這些字詞，請參閱「瞭解驗證和授權」。如要啟用這個選項，請參閱「建立存取憑證」。

  2. 使用標準 OAuth 2.0 流程，要求使用者同意授權，以取得 OAuth 2.0 存取權杖。詳情請參閱「瞭解驗證和授權」。

    如要使用這個選項，網域管理員必須在 Google 管理控制台中選取「允許在收發電子郵件時使用 S/MIME 加密功能」核取方塊。詳情請參閱「在管理控制台中啟用代管式 S/MIME」。

授權範圍

Gmail API 採用與 Gmail sendAs 方法相同的 OAuth 範圍：

  • gmail.settings.basic：更新主要 SendAs S/MIME 時必須提供。

  • gmail.settings.sharing：更新自訂 from S/MIME 時必須提供。

設定 S/MIME 金鑰

settings.sendAs.smimeInfo 資源提供多種管理 S/MIME 憑證的方法。每個憑證都與使用者的其中一個「以這個別名傳送郵件」別名相關聯。

如要判斷使用者的「以這個地址寄信」別名，請對 settings.sendAs 資源使用 settings.sendAs.list 方法。

上傳 S/MIME 金鑰

使用 settings.sendAs.smimeInfo 資源的 settings.sendAs.smimeInfo.insert 方法，為使用者的別名上傳新的 S/MIME 金鑰。使用下列路徑參數找出目標別名：

  • userId：使用者的電子郵件地址。使用特殊值 me 表示已驗證的使用者。

  • sendAsEmail：您要上傳金鑰的別名。使用這個別名傳送郵件時，這個電子郵件地址會顯示在 From: 標頭中。

以 PKCS #12 格式在 pkcs12 欄位中提供 S/MIME 憑證和私密金鑰。請勿在要求中設定任何其他欄位。pkcs12 欄位包含使用者 S/MIME 金鑰和簽署憑證鏈。API 會先對這個欄位執行標準驗證，再接受該欄位，並驗證下列事項：

  • 主旨與指定的電子郵件地址相符。
  • 到期日有效。
  • 核發憑證授權單位 (CA) 位於 Google 信任清單中。
  • 憑證符合 Gmail 的技術限制。

如果金鑰已加密，請在「encryptedKeyPassword」欄位中提供密碼。成功呼叫 settings.sendAs.smimeInfo.insert 方法會傳回 settings.sendAs.smimeInfo 資源 id，用於日後參照金鑰。

列出使用者的 S/MIME 金鑰

在 settings.sendAs.smimeInfo 資源上使用 settings.sendAs.smimeInfo.list 方法，傳回指定別名和使用者的 S/MIME 金鑰清單。使用下列路徑參數找出目標別名：

  • userId：使用者的電子郵件地址。使用特殊值 me 表示已驗證的使用者。

  • sendAsEmail：要列出金鑰的別名。使用這個別名傳送郵件時，這個電子郵件地址會顯示在 From: 標頭中。

擷取別名的 S/MIME 金鑰

在 settings.sendAs.smimeInfo 資源上使用 settings.sendAs.smimeInfo.get 方法，即可傳回使用者的特定「以其他地址或別名傳送郵件」別名的特定 S/MIME 金鑰。使用下列路徑參數找出目標別名：

  • userId：使用者的電子郵件地址。使用特殊值 me 表示已驗證的使用者。

  • sendAsEmail：要擷取金鑰的別名。使用這個別名傳送郵件時，這個電子郵件地址會顯示在 From: 標頭中。

刪除 S/MIME 金鑰

在 settings.sendAs.smimeInfo 資源上使用 settings.sendAs.smimeInfo.delete 方法，從別名中刪除指定的 S/MIME 金鑰。使用下列路徑參數找出目標別名：

  • userId：使用者的電子郵件地址。使用特殊值 me 表示已驗證的使用者。

  • sendAsEmail：要從中刪除金鑰的別名。使用這個別名傳送郵件時，這個電子郵件地址會顯示在 From: 標頭中。

  • id：smimeInfo 的不可變更 ID。

刪除金鑰後，系統就不會再顯示或使用該金鑰。您無法解密使用對應公開金鑰加密的 S/MIME 郵件。刪除金鑰前，請先向核發機構 (CA) 撤銷金鑰。

為別名設定預設 S/MIME 金鑰

使用 settings.sendAs.smimeInfo 資源的 settings.sendAs.smimeInfo.setDefault 方法，將指定的 S/MIME 金鑰標示為指定別名的預設金鑰。使用下列路徑參數找出目標別名：

  • userId：使用者的電子郵件地址。使用特殊值 me 表示已驗證的使用者。

  • sendAsEmail：要設定預設金鑰的別名。使用這個別名傳送郵件時，這個電子郵件地址會顯示在 From: 標頭中。

  • id：smimeInfo 的不可變更 ID。

使用者的「以這個地址傳送郵件」別名只能有一個預設的 S/MIME 金鑰。呼叫 settings.sendAs.smimeInfo.setDefault 方法會取消先前的預設值。

使用者收到以特定金鑰簽署的 S/MIME 郵件時，Gmail 會將該金鑰與最遠的not_before有效日期建立關聯，並在加密傳送給相關使用者的郵件時，預設使用該金鑰。如要確保使用者已與之通訊的 Gmail 使用者採用新的預設金鑰，請確認新的預設金鑰的 not_before 日期晚於先前的預設金鑰，或撤銷先前的預設金鑰。

程式碼範例

下列程式碼範例說明如何使用 Gmail API，管理多位使用者的機構 S/MIME 憑證：

為 S/MIME 憑證建立 smimeInfo 資源

這個程式碼範例說明如何從檔案讀取憑證、將憑證編碼為 Base64URL 字串，並指派給 settings.sendAs.smimeInfo 資源的 pkcs12 欄位：

Java

gmail/snippets/src/main/java/CreateSmimeInfo.java
import com.google.api.services.gmail.model.SmimeInfo;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Base64;

/* Class to demonstrate the use of Gmail Create SmimeInfo API */
public class CreateSmimeInfo {
  /**
   * Create an SmimeInfo resource for a certificate from file.
   *
   * @param filename Name of the file containing the S/MIME certificate.
   * @param password Password for the certificate file, or null if the file is not
   *                 password-protected.
   * @return An SmimeInfo object with the specified certificate.
   */
  public static SmimeInfo createSmimeInfo(String filename, String password) {
    SmimeInfo smimeInfo = null;
    InputStream in = null;

    try {
      File file = new File(filename);
      in = new FileInputStream(file);
      byte[] fileContent = new byte[(int) file.length()];
      in.read(fileContent);

      smimeInfo = new SmimeInfo();
      smimeInfo.setPkcs12(Base64.getUrlEncoder().encodeToString(fileContent));
      if (password != null && password.length() > 0) {
        smimeInfo.setEncryptedKeyPassword(password);
      }
    } catch (Exception e) {
      System.out.printf("An error occured while reading the certificate file: %s\n", e);
    } finally {
      try {
        if (in != null) {
          in.close();
        }
      } catch (IOException ioe) {
        System.out.printf("An error occured while closing the input stream: %s\n", ioe);
      }
    }
    return smimeInfo;
  }
}

Python

gmail/snippet/smime snippets/create_smime_info.py
import base64


def create_smime_info(cert_filename, cert_password):
  """Create an smimeInfo resource for a certificate from file.
  Args:
    cert_filename: Name of the file containing the S/MIME certificate.
    cert_password: Password for the certificate file, or None if the file is not
        password-protected.
  Returns : Smime object, including smime information
  """

  smime_info = None
  try:
    with open(cert_filename, "rb") as cert:
      smime_info = {}
      data = cert.read().encode("UTF-8")
      smime_info["pkcs12"] = base64.urlsafe_b64encode(data).decode()
      if cert_password and len(cert_password) > 0:
        smime_info["encryptedKeyPassword"] = cert_password

  except (OSError, IOError) as error:
    print(f"An error occurred while reading the certificate file: {error}")
    smime_info = None

  return smime_info


if __name__ == "__main__":
  print(create_smime_info(cert_filename="xyz", cert_password="xyz"))

上傳 S/MIME 憑證

如要上傳憑證，請呼叫 settings.sendAs.smimeInfo.insert 方法，並在要求主體中提供 settings.sendAs.smimeInfo 資源：

Java

gmail/snippets/src/main/java/InsertSmimeInfo.java
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.gmail.Gmail;
import com.google.api.services.gmail.GmailScopes;
import com.google.api.services.gmail.model.SmimeInfo;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import java.io.IOException;

/* Class to demonstrate the use of Gmail Insert Smime Certificate API*/
public class InsertSmimeInfo {
  /**
   * Upload an S/MIME certificate for the user.
   *
   * @param userId      User's email address.
   * @param sendAsEmail The "send as" email address, or null if it should be the same as userId.
   * @param smimeInfo   The SmimeInfo object containing the user's S/MIME certificate.
   * @return An SmimeInfo object with details about the uploaded certificate, {@code null} otherwise.
   * @throws IOException - if service account credentials file not found.
   */
  public static SmimeInfo insertSmimeInfo(String userId,
                                          String sendAsEmail,
                                          SmimeInfo smimeInfo)
      throws IOException {
        /* Load pre-authorized user credentials from the environment.
           TODO(developer) - See https://developers.google.com/identity for
            guides on implementing OAuth2 for your application. */
    GoogleCredentials credentials = GoogleCredentials.getApplicationDefault()
        .createScoped(GmailScopes.GMAIL_SETTINGS_SHARING);
    HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(
        credentials);

    // Create the gmail API client
    Gmail service = new Gmail.Builder(new NetHttpTransport(),
        GsonFactory.getDefaultInstance(),
        requestInitializer)
        .setApplicationName("Gmail samples")
        .build();

    if (sendAsEmail == null) {
      sendAsEmail = userId;
    }

    try {
      SmimeInfo results = service.users().settings().sendAs().smimeInfo()
          .insert(userId, sendAsEmail, smimeInfo)
          .execute();
      System.out.printf("Inserted certificate, id: %s\n", results.getId());
      return results;
    } catch (IOException e) {
      System.err.printf("An error occured: %s", e);
    }
    return null;
  }
}

Python

gmail/snippet/smime snippets/insert_smime_info.py
import create_smime_info
import google.auth
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError


def insert_smime_info():
  """Upload an S/MIME certificate for the user.
  Print the inserted certificate's id
  Returns : Result object with inserted certificate id and other meta-data

  Load pre-authorized user credentials from the environment.
  TODO(developer) - See https://developers.google.com/identity
  for guides on implementing OAuth2 for the application.
  """
  creds, _ = google.auth.default()

  try:
    # create gmail api client
    service = build("gmail", "v1", credentials=creds)

    user_id = "gduser1@workspacesamples.dev"
    smime_info = create_smime_info.create_smime_info(
        cert_filename="xyz", cert_password="xyz"
    )
    send_as_email = None

    if not send_as_email:
      send_as_email = user_id

    # pylint: disable=maybe-no-member
    results = (
        service.users()
        .settings()
        .sendAs()
        .smimeInfo()
        .insert(userId=user_id, sendAsEmail=send_as_email, body=smime_info)
        .execute()
    )
    print(f'Inserted certificate; id: {results["id"]}')

  except HttpError as error:
    print(f"An error occurred: {error}")
    results = None

  return results


if __name__ == "__main__":
  insert_smime_info()

管理多位使用者的憑證

下列程式碼範例說明如何透過單一批次呼叫，管理機構中多位使用者的憑證：

從 CSV 檔案插入認證

以下是 CSV 檔案範例，列出使用者 ID 和每個使用者憑證的路徑：

$ cat certificates.csv
user1@example.com,/path/to/user1_cert.p12,cert_password_1
user2@example.com,/path/to/user2_cert.p12,cert_password_2
user3@example.com,/path/to/user3_cert.p12,cert_password_3

Java

您可以透過 CreateSmimeInfo 和 InsertSmimeInfo 範例，上傳 CSV 檔案中指定使用者的憑證：

gmail/snippets/src/main/java/InsertCertFromCsv.java
import com.google.api.services.gmail.model.SmimeInfo;
import java.io.File;
import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVRecord;

/* Class to demonstrate the use of Gmail Insert Certificate from CSV File */
public class InsertCertFromCsv {
  /**
   * Upload S/MIME certificates based on the contents of a CSV file.
   *
   * <p>Each row of the CSV file should contain a user ID, path to the certificate, and the
   * certificate password.
   *
   * @param csvFilename Name of the CSV file.
   */
  public static void insertCertFromCsv(String csvFilename) {
    try {
      File csvFile = new File(csvFilename);
      CSVParser parser =
          CSVParser.parse(csvFile, java.nio.charset.StandardCharsets.UTF_8, CSVFormat.DEFAULT);
      for (CSVRecord record : parser) {
        String userId = record.get(0);
        String certFilename = record.get(1);
        String certPassword = record.get(2);
        SmimeInfo smimeInfo = CreateSmimeInfo.createSmimeInfo(certFilename,
            certPassword);
        if (smimeInfo != null) {
          InsertSmimeInfo.insertSmimeInfo(userId,
              userId,
              smimeInfo);
        } else {
          System.err.printf("Unable to read certificate file for userId: %s\n", userId);
        }
      }
    } catch (Exception e) {
      System.err.printf("An error occured while reading the CSV file: %s", e);
    }
  }
}

Python

您可以透過 create_smime_info 和 insert_smime_info 範例，上傳 CSV 檔案中指定使用者的憑證：

gmail/snippet/smime snippets/insert_cert_from_csv.py
import csv

import create_smime_info
import insert_smime_info


def insert_cert_from_csv(csv_filename):
  """Upload S/MIME certificates based on the contents of a CSV file.
  Each row of the CSV file should contain a user ID, path to the certificate,
  and the certificate password.

  Args:
    csv_filename: Name of the CSV file.
  """

  try:
    with open(csv_filename, "rb") as cert:
      csv_reader = csv.reader(cert, delimiter=",")
      next(csv_reader, None)  # skip CSV file header
      for row in csv_reader:
        user_id = row[0]
        cert_filename = row[1]
        cert_password = row[2]
        smime_info = create_smime_info.create_smime_info(
            cert_filename=cert_filename, cert_password=cert_password
        )
        if smime_info:
          insert_smime_info.insert_smime_info()
        else:
          print(f"Unable to read certificate file for user_id: {user_id}")
        return smime_info

  except (OSError, IOError) as error:
    print(f"An error occured while reading the CSV file: {error}")


if __name__ == "__main__":
  insert_cert_from_csv(csv_filename="xyz")

憑證管理功能

這個範例結合了 settings.sendAs.smimeInfo 資源中的幾種方法，說明如何管理貴機構的憑證。列出使用者的憑證。如果預設憑證已過期或未設定，系統會上傳指定檔案中的憑證。然後將到期日最晚的憑證設為預設憑證。

這個函式會處理 CSV 檔案，與先前的「從 CSV 檔案插入認證」範例類似。

Java

gmail/snippets/src/main/java/UpdateSmimeCerts.java
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.gmail.Gmail;
import com.google.api.services.gmail.GmailScopes;
import com.google.api.services.gmail.model.ListSmimeInfoResponse;
import com.google.api.services.gmail.model.SmimeInfo;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import java.io.IOException;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;

/* Class to demonstrate the use of Gmail Update Smime Certificate API*/
public class UpdateSmimeCerts {
  /**
   * Update S/MIME certificates for the user.
   *
   * <p>First performs a lookup of all certificates for a user. If there are no certificates, or
   * they all expire before the specified date/time, uploads the certificate in the specified file.
   * If the default certificate is expired or there was no default set, chooses the certificate with
   * the expiration furthest into the future and sets it as default.
   *
   * @param userId       User's email address.
   * @param sendAsEmail  The "send as" email address, or None if it should be the same as user_id.
   * @param certFilename Name of the file containing the S/MIME certificate.
   * @param certPassword Password for the certificate file, or None if the file is not
   *                     password-protected.
   * @param expireTime   DateTime object against which the certificate expiration is compared. If
   *                     None, uses the current time. @ returns: The ID of the default certificate.
   * @return The ID of the default certificate, {@code null} otherwise.
   * @throws IOException - if service account credentials file not found.
   */
  public static String updateSmimeCerts(String userId,
                                        String sendAsEmail,
                                        String certFilename,
                                        String certPassword,
                                        LocalDateTime expireTime)
      throws IOException {
        /* Load pre-authorized user credentials from the environment.
           TODO(developer) - See https://developers.google.com/identity for
            guides on implementing OAuth2 for your application. */
    GoogleCredentials credentials = GoogleCredentials.getApplicationDefault()
        .createScoped(GmailScopes.GMAIL_SETTINGS_SHARING);
    HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(
        credentials);

    // Create the gmail API client
    Gmail service = new Gmail.Builder(new NetHttpTransport(),
        GsonFactory.getDefaultInstance(),
        requestInitializer)
        .setApplicationName("Gmail samples")
        .build();

    if (sendAsEmail == null) {
      sendAsEmail = userId;
    }

    ListSmimeInfoResponse listResults;
    try {
      listResults =
          service.users().settings().sendAs().smimeInfo().list(userId, sendAsEmail).execute();
    } catch (IOException e) {
      System.err.printf("An error occurred during list: %s\n", e);
      return null;
    }

    String defaultCertId = null;
    String bestCertId = null;
    LocalDateTime bestCertExpire = LocalDateTime.MIN;

    if (expireTime == null) {
      expireTime = LocalDateTime.now();
    }
    if (listResults != null && listResults.getSmimeInfo() != null) {
      for (SmimeInfo smimeInfo : listResults.getSmimeInfo()) {
        String certId = smimeInfo.getId();
        boolean isDefaultCert = smimeInfo.getIsDefault();
        if (isDefaultCert) {
          defaultCertId = certId;
        }
        LocalDateTime exp =
            LocalDateTime.ofInstant(
                Instant.ofEpochMilli(smimeInfo.getExpiration()), ZoneId.systemDefault());
        if (exp.isAfter(expireTime)) {
          if (exp.isAfter(bestCertExpire)) {
            bestCertId = certId;
            bestCertExpire = exp;
          }
        } else {
          if (isDefaultCert) {
            defaultCertId = null;
          }
        }
      }
    }
    if (defaultCertId == null) {
      String defaultId = bestCertId;
      if (defaultId == null && certFilename != null) {
        SmimeInfo smimeInfo = CreateSmimeInfo.createSmimeInfo(certFilename,
            certPassword);
        SmimeInfo insertResults = InsertSmimeInfo.insertSmimeInfo(userId,
            sendAsEmail,
            smimeInfo);
        if (insertResults != null) {
          defaultId = insertResults.getId();
        }
      }

      if (defaultId != null) {
        try {
          service.users().settings().sendAs().smimeInfo().setDefault(userId, sendAsEmail, defaultId)
              .execute();
          return defaultId;
        } catch (IOException e) {
          System.err.printf("An error occured during setDefault: %s", e);
        }
      }
    } else {
      return defaultCertId;
    }

    return null;
  }
}

Python

gmail/snippet/smime snippets/update_smime_cert.py
from datetime import datetime

import create_smime_info
import google.auth
import insert_smime_info
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError


def update_smime_cert(
    user_id, send_as_email, cert_filename, cert_password, expire_dt
):
  """Update S/MIME certificates for the user.

  First performs a lookup of all certificates for a user.  If there are no
  certificates, or they all expire before the specified date/time, uploads the
  certificate in the specified file.  If the default certificate is expired or
  there was no default set, chooses the certificate with the expiration furthest
  into the future and sets it as default.

  Args:
    user_id: User's email address.
    send_as_email: The "send as" email address, or None if it should be the same
        as user_id.
    cert_filename: Name of the file containing the S/MIME certificate.
    cert_password: Password for the certificate file, or None if the file is not
        password-protected.
    expire_dt: DateTime object against which the certificate expiration is
      compared.  If None, uses the current time.

  Returns:
    The ID of the default certificate.

  Load pre-authorized user credentials from the environment.
  TODO(developer) - See https://developers.google.com/identity
  for guides on implementing OAuth2 for the application.
  """
  if not send_as_email:
    send_as_email = user_id

  creds, _ = google.auth.default()

  try:
    # create gmail api client
    service = build("gmail", "v1", credentials=creds)

    # pylint: disable=maybe-no-member
    results = (
        service.users()
        .settings()
        .sendAs()
        .smimeInfo()
        .list(userId=user_id, sendAsEmail=send_as_email)
        .execute()
    )

  except HttpError as error:
    print(f"An error occurred during list: {error}")
    return None

  default_cert_id = None
  best_cert_id = (None, datetime.datetime.fromtimestamp(0))

  if not expire_dt:
    expire_dt = datetime.datetime.now()
  if results and "smimeInfo" in results:
    for smime_info in results["smimeInfo"]:
      cert_id = smime_info["id"]
      is_default_cert = smime_info["isDefault"]
      if is_default_cert:
        default_cert_id = cert_id
      exp = datetime.datetime.fromtimestamp(smime_info["expiration"] / 1000)
      if exp > expire_dt:
        if exp > best_cert_id[1]:
          best_cert_id = (cert_id, exp)
      else:
        if is_default_cert:
          default_cert_id = None

  if not default_cert_id:
    default_id = best_cert_id[0]
    if not default_id and cert_filename:
      create_smime_info.create_smime_info(
          cert_filename=cert_filename, cert_password=cert_password
      )
      results = insert_smime_info.insert_smime_info()
      if results:
        default_id = results["id"]

    if default_id:
      try:
        # pylint: disable=maybe-no-member
        service.users().settings().sendAs().smimeInfo().setDefault(
            userId=user_id, sendAsEmail=send_as_email, id=default_id
        ).execute()
        return default_id
      except HttpError as error:
        print(f"An error occurred during setDefault: {error}")
  else:
    return default_cert_id

  return None


if __name__ == "__main__":
  update_smime_cert(
      user_id="xyz",
      send_as_email=None,
      cert_filename="xyz",
      cert_password="xyz",
      expire_dt=None,
  )