Authenticating as a service account

This topic explains how to authenticate an application as a service account. For general information about authentication to Google Cloud APIs, including common authentication scenarios and strategies, see Authentication overview. For more information about service accounts, see service accounts in the Identity and Access Management documentation.

Finding credentials automatically

If your application runs inside a Google Cloud environment, and you have attached a service account to that environment, your application can retrieve credentials for the service account. The application can then use the credentials to call Google Cloud APIs.

You can attach service accounts to resources for many different Google Cloud services, including Compute Engine, Google Kubernetes Engine, App Engine, Cloud Run, and Cloud Functions. We recommend using this strategy because it is more convenient and secure than manually passing credentials.

Additionally, we recommend you use Google Cloud Client Libraries for your application. Google Cloud Client Libraries use a library called Application Default Credentials (ADC) to automatically find your service account credentials. ADC looks for service account credentials in the following order:

  1. If the environment variable GOOGLE_APPLICATION_CREDENTIALS is set, ADC uses the service account key or configuration file that the variable points to.

  2. If the environment variable GOOGLE_APPLICATION_CREDENTIALS isn't set, ADC uses the service account that is attached to the resource that is running your code.

    This service account might be a default service account provided by Compute Engine, Google Kubernetes Engine, App Engine, Cloud Run, or Cloud Functions. It might also be a user-managed service account that you created.

  3. If ADC can't use any of the above credentials, an error occurs.

The following code example illustrates how to use the ADC library in your application code. To run this example, you must install the Cloud Storage client library.

C#

public object AuthImplicit(string projectId)
{
    // If you don't specify credentials when constructing the client, the
    // client library will look for credentials in the environment.
    var credential = GoogleCredential.GetApplicationDefault();
    var storage = StorageClient.Create(credential);
    // Make an authenticated API request.
    var buckets = storage.ListBuckets(projectId);
    foreach (var bucket in buckets)
    {
        Console.WriteLine(bucket.Name);
    }
    return null;
}

Go


// implicit uses Application Default Credentials to authenticate.
func implicit() {
	ctx := context.Background()

	// For API packages whose import path is starting with "cloud.google.com/go",
	// such as cloud.google.com/go/storage in this case, if there are no credentials
	// provided, the client library will look for credentials in the environment.
	storageClient, err := storage.NewClient(ctx)
	if err != nil {
		log.Fatal(err)
	}
	defer storageClient.Close()

	it := storageClient.Buckets(ctx, "project-id")
	for {
		bucketAttrs, err := it.Next()
		if err == iterator.Done {
			break
		}
		if err != nil {
			log.Fatal(err)
		}
		fmt.Println(bucketAttrs.Name)
	}

	// For packages whose import path is starting with "google.golang.org/api",
	// such as google.golang.org/api/cloudkms/v1, use NewService to create the client.
	kmsService, err := cloudkms.NewService(ctx)
	if err != nil {
		log.Fatal(err)
	}

	_ = kmsService
}

Java

static void authImplicit() {
  // If you don't specify credentials when constructing the client, the client library will
  // look for credentials via the environment variable GOOGLE_APPLICATION_CREDENTIALS.
  Storage storage = StorageOptions.getDefaultInstance().getService();

  System.out.println("Buckets:");
  Page<Bucket> buckets = storage.list();
  for (Bucket bucket : buckets.iterateAll()) {
    System.out.println(bucket.toString());
  }
}

Node.js

// Imports the Google Cloud client library.
const {Storage} = require('@google-cloud/storage');

// Instantiates a client. If you don't specify credentials when constructing
// the client, the client library will look for credentials in the
// environment.
const storage = new Storage();
// Makes an authenticated API request.
async function listBuckets() {
  try {
    const results = await storage.getBuckets();

    const [buckets] = results;

    console.log('Buckets:');
    buckets.forEach(bucket => {
      console.log(bucket.name);
    });
  } catch (err) {
    console.error('ERROR:', err);
  }
}
listBuckets();

PHP

// Imports the Cloud Storage client library.
use Google\Cloud\Storage\StorageClient;

/**
 * Authenticate to a cloud client library using a service account implicitly.
 *
 * @param string $projectId The Google project ID.
 */
function auth_cloud_implicit($projectId)
{
    $config = [
        'projectId' => $projectId,
    ];

    # If you don't specify credentials when constructing the client, the
    # client library will look for credentials in the environment.
    $storage = new StorageClient($config);

    # Make an authenticated API request (listing storage buckets)
    foreach ($storage->buckets() as $bucket) {
        printf('Bucket: %s' . PHP_EOL, $bucket->name());
    }
}

Python

def implicit():
    from google.cloud import storage

    # If you don't specify credentials when constructing the client, the
    # client library will look for credentials in the environment.
    storage_client = storage.Client()

    # Make an authenticated API request
    buckets = list(storage_client.list_buckets())
    print(buckets)

Ruby

# project_id = "Your Google Cloud project ID"

require "google/cloud/storage"

# If you don't specify credentials when constructing the client, the client
# library will look for credentials in the environment.
storage = Google::Cloud::Storage.new project: project_id

# Make an authenticated API request
storage.buckets.each do |bucket|
  puts bucket.name
end

Passing credentials manually

If your application runs in an environment with no service account attached, such as on-premises or on another cloud provider, you should use workload identity federation.

If you can't use workload identity federation, then you must create a service account and one or more service account keys, which are credentials associated with the service account. Service account keys can then be manually passed to your application.

Make sure you review the best practices for managing service account keys.

Creating a service account

The following steps describe how to create a service account if you don't have one:

Console

Create a service account:

  1. In the Cloud console, go to the Create service account page.

    Go to Create service account
  2. Select your project.

  3. In the Service account name field, enter a name. The Cloud console fills in the Service account ID field based on this name.

    In the Service account description field, enter a description. For example, Service account for quickstart.

  4. Click Create and continue.

  5. To provide access to your project, grant the following role(s) to your service account: Project > Owner.

    In the Select a role list, select a role.

    For additional roles, click Add another role and add each additional role.

  6. Click Continue.

  7. Click Done to finish creating the service account.

    Do not close your browser window. You will use it in the next step.

Create a service account key:

  1. In the Cloud console, click the email address for the service account that you created.
  2. Click Keys.
  3. Click Add key, and then click Create new key.
  4. Click Create. A JSON key file is downloaded to your computer.
  5. Click Close.

gcloud

Set up authentication:

  1. Create the service account. Replace NAME with a name for the service account: 

    gcloud iam service-accounts create NAME

  2. Grant roles to the service account. Run the following command once for each of the following IAM roles: roles/owner: 

    gcloud projects add-iam-policy-binding PROJECT_ID --member="serviceAccount:SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com" --role=ROLE

    Replace the following:

    • SERVICE_ACCOUNT_NAME: the name of the service account
    • PROJECT_ID: the project ID where you created the service account
    • ROLE: the role to grant

  3. Generate the key file: 

    gcloud iam service-accounts keys create FILE_NAME.json --iam-account=SERVICE_ACCOUNT_NAME@PROJECT_ID.iam.gserviceaccount.com

    Replace the following:

    • FILE_NAME: a name for the key file
    • SERVICE_ACCOUNT_NAME: the name of the service account
    • PROJECT_ID: the project ID where you created the service account

Passing credentials via environment variable

Provide authentication credentials to your application code by setting the environment variable GOOGLE_APPLICATION_CREDENTIALS. This variable applies only to your current shell session. If you want the variable to apply to future shell sessions, set the variable in your shell startup file, for example in the ~/.bashrc or ~/.profile file.

Linux or macOS

export GOOGLE_APPLICATION_CREDENTIALS="KEY_PATH"

Replace KEY_PATH with the path of the JSON file that contains your service account key.

For example:

export GOOGLE_APPLICATION_CREDENTIALS="/home/user/Downloads/service-account-file.json"

Windows

For PowerShell:

$env:GOOGLE_APPLICATION_CREDENTIALS="KEY_PATH"

Replace KEY_PATH with the path of the JSON file that contains your service account key.

For example:

$env:GOOGLE_APPLICATION_CREDENTIALS="C:\Users\username\Downloads\service-account-file.json"

For command prompt:

set GOOGLE_APPLICATION_CREDENTIALS=KEY_PATH

Replace KEY_PATH with the path of the JSON file that contains your service account key.

After you've completed the above steps, ADC can automatically find your credentials, as described in the section above. We recommend using ADC because it requires less code and your code is portable in different environments.

Passing credentials using code

You can alternately choose to explicitly point to your service account file in code, as shown in the following example. You must install the Cloud Storage client library to run the following example.

C#

        // Some APIs, like Storage, accept a credential in their Create()
        // method.
        public object AuthExplicit(string projectId, string jsonPath)
        {
            // Explicitly use service account credentials by specifying 
            // the private key file.
            var credential = GoogleCredential.FromFile(jsonPath);
            var storage = StorageClient.Create(credential);
            // Make an authenticated API request.
            var buckets = storage.ListBuckets(projectId);
            foreach (var bucket in buckets)
            {
                Console.WriteLine(bucket.Name);
            }
            return null;
        }
        // Other APIs, like Language, accept a channel in their Create()
        // method.
        public object AuthExplicit(string projectId, string jsonPath)
        {
            LanguageServiceClientBuilder builder = new LanguageServiceClientBuilder
            {
                CredentialsPath = jsonPath
            };

            LanguageServiceClient client = builder.Build();
            AnalyzeSentiment(client);
            return 0;
        }

Go


// explicit reads credentials from the specified path.
func explicit(jsonPath, projectID string) {
	ctx := context.Background()
	client, err := storage.NewClient(ctx, option.WithCredentialsFile(jsonPath))
	if err != nil {
		log.Fatal(err)
	}
	defer client.Close()
	fmt.Println("Buckets:")
	it := client.Buckets(ctx, projectID)
	for {
		battrs, err := it.Next()
		if err == iterator.Done {
			break
		}
		if err != nil {
			log.Fatal(err)
		}
		fmt.Println(battrs.Name)
	}
}

Java

static void authExplicit(String jsonPath) throws IOException {
  // You can specify a credential file by providing a path to GoogleCredentials.
  // Otherwise credentials are read from the GOOGLE_APPLICATION_CREDENTIALS environment variable.
  GoogleCredentials credentials = GoogleCredentials.fromStream(new FileInputStream(jsonPath))
        .createScoped(Lists.newArrayList("https://www.googleapis.com/auth/cloud-platform"));
  Storage storage = StorageOptions.newBuilder().setCredentials(credentials).build().getService();

  System.out.println("Buckets:");
  Page<Bucket> buckets = storage.list();
  for (Bucket bucket : buckets.iterateAll()) {
    System.out.println(bucket.toString());
  }
}

Node.js

// Imports the Google Cloud client library.
const {Storage} = require('@google-cloud/storage');

// Instantiates a client. Explicitly use service account credentials by
// specifying the private key file. All clients in google-cloud-node have this
// helper, see https://github.com/GoogleCloudPlatform/google-cloud-node/blob/master/docs/authentication.md
// const projectId = 'project-id'
// const keyFilename = '/path/to/keyfile.json'
const storage = new Storage({projectId, keyFilename});

// Makes an authenticated API request.
async function listBuckets() {
  try {
    const [buckets] = await storage.getBuckets();

    console.log('Buckets:');
    buckets.forEach(bucket => {
      console.log(bucket.name);
    });
  } catch (err) {
    console.error('ERROR:', err);
  }
}
listBuckets();

PHP

namespace Google\Cloud\Samples\Auth;

// Imports the Cloud Storage client library.
use Google\Cloud\Storage\StorageClient;

/**
 * Authenticate to a cloud client library using a service account explicitly.
 *
 * @param string $projectId           The Google project ID.
 * @param string $serviceAccountPath  Path to service account credentials JSON.
 */
function auth_cloud_explicit($projectId, $serviceAccountPath)
{
    # Explicitly use service account credentials by specifying the private key
    # file.
    $config = [
        'keyFilePath' => $serviceAccountPath,
        'projectId' => $projectId,
    ];
    $storage = new StorageClient($config);

    # Make an authenticated API request (listing storage buckets)
    foreach ($storage->buckets() as $bucket) {
        printf('Bucket: %s' . PHP_EOL, $bucket->name());
    }
}

Python

def explicit():
    from google.cloud import storage

    # Explicitly use service account credentials by specifying the private key
    # file.
    storage_client = storage.Client.from_service_account_json(
        'service_account.json')

    # Make an authenticated API request
    buckets = list(storage_client.list_buckets())
    print(buckets)

Ruby

# project_id = "Your Google Cloud project ID"
# key_file   = "path/to/service-account.json"
require "google/cloud/storage"

# Explicitly use service account credentials by specifying the private key
# file.
storage = Google::Cloud::Storage.new project: project_id, keyfile: key_file

# Make an authenticated API request
storage.buckets.each do |bucket|
  puts bucket.name
end

Troubleshooting API errors

Learn more about how to troubleshoot failed API requests at Cloud APIs errors.

What's next

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