此方法使用 Gmail API、OAuth2 for Apps 脚本库和“域范围授权”，这是 G Suite 管理员代表其域内的用户进行 API 调用的一种方式。
Step 1:确保适用于应用程序脚本的 OAuth2 https://github.com/googlesamples/apps-script-oauth2库已添加到您的项目中。
Step 2:设置“域范围内的授权”。有一个页面here https://developers.google.com/drive/v2/web/delegation解释了如何为 Drive API 执行此操作，但对于任何 Google API（包括 Gmail API）来说几乎都是相同的。按照该页面上的步骤进行操作，直到“将域范围的权限委派给您的服务帐户”步骤（包括该步骤）。
Step 3:下面的代码包括如何在前面的步骤完成后设置签名：
function setSignatureTest() {
var email = '[email protected] /cdn-cgi/l/email-protection';
var signature = 'test signature';
var test = setSignature(email, signature);
Logger.log('test result: ' + test);
}
function setSignature(email, signature) {
Logger.log('starting setSignature');
var signatureSetSuccessfully = false;
var service = getDomainWideDelegationService('Gmail: ', 'https://www.googleapis.com/auth/gmail.settings.basic', email);
if (!service.hasAccess()) {
Logger.log('failed to authenticate as user ' + email);
Logger.log(service.getLastError());
signatureSetSuccessfully = service.getLastError();
return signatureSetSuccessfully;
} else Logger.log('successfully authenticated as user ' + email);
var username = email.split("@")[0];
var resource = { signature: signature };
var requestBody = {};
requestBody.headers = {'Authorization': 'Bearer ' + service.getAccessToken()};
requestBody.contentType = "application/json";
requestBody.method = "PUT";
requestBody.payload = JSON.stringify(resource);
requestBody.muteHttpExceptions = false;
var emailForUrl = encodeURIComponent(email);
var url = 'https://www.googleapis.com/gmail/v1/users/me/settings/sendAs/' + emailForUrl;
var maxSetSignatureAttempts = 20;
var currentSetSignatureAttempts = 0;
do {
try {
currentSetSignatureAttempts++;
Logger.log('currentSetSignatureAttempts: ' + currentSetSignatureAttempts);
var setSignatureResponse = UrlFetchApp.fetch(url, requestBody);
Logger.log('setSignatureResponse on successful attempt:' + setSignatureResponse);
signatureSetSuccessfully = true;
break;
} catch(e) {
Logger.log('set signature failed attempt, waiting 3 seconds and re-trying');
Utilities.sleep(3000);
}
if (currentSetSignatureAttempts >= maxSetSignatureAttempts) {
Logger.log('exceeded ' + maxSetSignatureAttempts + ' set signature attempts, deleting user and ending script');
throw new Error('Something went wrong when setting their email signature.');
}
} while (!signatureSetSuccessfully);
return signatureSetSuccessfully;
}
// these two things are included in the .JSON file that you download when creating the service account and service account key
var OAUTH2_SERVICE_ACCOUNT_PRIVATE_KEY = '-----BEGIN PRIVATE KEY-----\nxxxxxxxxxxxxxxxxxxxxx\n-----END PRIVATE KEY-----\n';
var OAUTH2_SERVICE_ACCOUNT_CLIENT_EMAIL = 'xxxxxxxxxxxxxxxxxxxxx.iam.gserviceaccount.com';
function getDomainWideDelegationService(serviceName, scope, email) {
Logger.log('starting getDomainWideDelegationService for email: ' + email);
return OAuth2.createService(serviceName + email)
// Set the endpoint URL.
.setTokenUrl('https://accounts.google.com/o/oauth2/token')
// Set the private key and issuer.
.setPrivateKey(OAUTH2_SERVICE_ACCOUNT_PRIVATE_KEY)
.setIssuer(OAUTH2_SERVICE_ACCOUNT_CLIENT_EMAIL)
// Set the name of the user to impersonate. This will only work for
// Google Apps for Work/EDU accounts whose admin has setup domain-wide
// delegation:
// https://developers.google.com/identity/protocols/OAuth2ServiceAccount#delegatingauthority
.setSubject(email)
// Set the property store where authorized tokens should be persisted.
.setPropertyStore(PropertiesService.getScriptProperties())
// Set the scope. This must match one of the scopes configured during the
// setup of domain-wide delegation.
.setScope(scope);
}
请注意：do-while 循环与maxSetSignatureAttempts and currentSetSignatureAttempts变量不是必需的。我添加它是因为，如果您在创建 Google 帐户并分配 G Suite 许可证后尝试立即设置签名，有时 Gmail API 会返回错误，就好像用户尚未创建一样。如果出现错误，do-while 循环基本上会等待 3 秒，然后重试，最多 x 次。如果您为现有用户设置签名，则不应遇到此问题。另外，本来我只是固定10秒睡眠，但大多数时候不需要那么长时间，但其他时候仍然会失败。所以这个循环比固定的睡眠量要好。
