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 that has a default service account, your application can retrieve the service account credentials to call Google Cloud APIs. Such environments include 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:

If the environment variable GOOGLE_APPLICATION_CREDENTIALS is set, ADC uses the service account file that the variable points to.
If the environment variable GOOGLE_APPLICATION_CREDENTIALS isn't set, ADC uses the default service account that Compute Engine, Google Kubernetes Engine, App Engine, Cloud Run, and Cloud Functions provide.
If ADC can't use either of the above credentials, an error occurs.

The following code example illustrates how to use the ADC library in your application code:

C#

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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

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// 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)
	}

	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

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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

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// 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

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

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

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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

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# 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 outside Google Cloud environments that provide a default service account, you need to manually create one. Then you can create 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.

Creating a service account

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

Cloud Console

In the Cloud Console, go to the Create service account key page.
Go to the Create Service Account Key page
From the Service account list, select New service account.
In the Service account name field, enter a name.
From the Role list, select Project > Owner.

Note: The Role field authorizes your service account to access resources. You can view and change this field later by using the Cloud Console. If you are developing a production app, specify more granular permissions than Project > Owner. For more information, see granting roles to service accounts.
Click Create. A JSON file that contains your key downloads to your computer.

Command line

You can run the following commands using the Cloud SDK on your local machine, or in Cloud Shell.

Create the service account. Replace [NAME] with a name for the service account.
```
gcloud iam service-accounts create [NAME]
```
Grant permissions to the service account. Replace [PROJECT_ID] with your project ID.
```
gcloud projects add-iam-policy-binding [PROJECT_ID] --member "serviceAccount:[NAME]@[PROJECT_ID].iam.gserviceaccount.com" --role "roles/owner"
```
Note: The Role field authorizes your service account to access resources. You can view and change this field later by using Cloud Console. If you are developing a production app, specify more granular permissions than Project > Owner. For more information, see granting roles to service accounts.

Generate the key file. Replace [FILE_NAME] with a name for the key file.

gcloud iam service-accounts keys create [FILE_NAME].json --iam-account [NAME]@[PROJECT_ID].iam.gserviceaccount.com

Passing credentials via environment variable

Provide authentication credentials to your application code by setting the environment variable GOOGLE_APPLICATION_CREDENTIALS. Replace [PATH] with the file path of the JSON file that contains your service account key. This variable only applies to your current shell session, so if you open a new session, set the variable again.

Linux or macOS

export GOOGLE_APPLICATION_CREDENTIALS="[PATH]"

For example:

export GOOGLE_APPLICATION_CREDENTIALS="/home/user/Downloads/my-key.json"

Windows

With PowerShell:

$env:GOOGLE_APPLICATION_CREDENTIALS="[PATH]"

For example:

$env:GOOGLE_APPLICATION_CREDENTIALS="C:\Users\username\Downloads\my-key.json"

With command prompt:

set GOOGLE_APPLICATION_CREDENTIALS=[PATH]

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#

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        // 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

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// 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)
	}
	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

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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

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// 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

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namespace Google\Cloud\Samples\Auth;

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

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

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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

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# 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

Best practices for managing credentials

Credentials provide access to sensitive data. The following practices help protect access to your credentials.

Do not embed secrets related to authentication in source code, such as API keys, OAuth tokens, and service account keys. You can use an environment variable pointing to credentials outside of the application's source code, such as Cloud Key Management Service.
Create and use different credentials for different contexts, such as in testing and production environments.
Only transfer credentials over a secure channel such as HTTPS to prevent a third party from intercepting your credentials. Never transfer in clear text or as part of the URL.
Never embed long-lived credentials into your client-side application. For example, do not embed service account keys into a mobile app. Client-side apps can be examined and credentials can easily be found and used by a third party.
Revoke a token if you no longer need it.

Troubleshooting API errors

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

What's next

Learn about authenticating to a Google Cloud API
Learn about authenticating as an end user
Learn about using API keys