Getting Started with Authentication

This article shows the recommended way to authenticate to a Cloud API.

Authentication refers to the process of determining a client's identity. Authorization refers to the process of determining what permissions an authenticated client has for a set of resources. That is, authentication refers to who you are, and authorization refers to what you can do.

For authentication, we recommend using a service account: a Google account that is associated with your GCP project, as opposed to a specific user. Service accounts can be used for authentication regardless of where your code runs (locally, Compute Engine, App Engine, on premises, etc.). For more information about other authentication types, see authentication overview.

Creating a service account

GCP Console

  1. In the GCP Console, go to the Create service account key page.

    Go to the Create Service Account Key page
  2. From the Service account list, select New service account.
  3. In the Service account name field, enter a name.

  4. 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 GCP Console. If you are developing a production app, specify more granular permissions than Project > Owner. For more information, see granting roles to service accounts.
  5. 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.

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

    gcloud iam service-accounts create [NAME]

  2. 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 GCP Console. If you are developing a production app, specify more granular permissions than Project > Owner. For more information, see granting roles to service accounts.

  3. 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

Setting the environment variable

If you plan to use a service account, you need to set an 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, and [FILE_NAME] with the filename. 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/[FILE_NAME].json"

Windows

With PowerShell:

$env:GOOGLE_APPLICATION_CREDENTIALS="[PATH]"

For example:

$env:GOOGLE_APPLICATION_CREDENTIALS="C:\Users\username\Downloads\[FILE_NAME].json"

With command prompt:

set GOOGLE_APPLICATION_CREDENTIALS=[PATH]

Setting the environment variable allows you to provide credentials separately from your application, without making changes to application code when you deploy. Alternately, you can explicitly specify the path to the service account key file in your code. For more information, see the production guide.

Verifying authentication

After setting the environment variable, you don't need to explicitly specify your credentials in code when using a Google Cloud Client Library. The client library can determine your credentials implicitly. For this reason, you can verify that authentication works by setting the environment variable, and then running client library code, such as the following example. If the request succeeds, authentication works.

You must install the Cloud Storage client library to run the following example.

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)
	}

	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 the
	// golang.org/x/oauth2/google package as shown below.
	oauthClient, err := google.DefaultClient(ctx, cloudkms.CloudPlatformScope)
	if err != nil {
		log.Fatal(err)
	}

	kmsService, err := cloudkms.New(oauthClient)
	if err != nil {
		log.Fatal(err)
	}

	_ = kmsService
}

Java

// If you don't specify credentials when constructing the client, the
// client library will look for credentials in the environment.

Storage storage = StorageOptions.getDefaultInstance().getService();

Page<Bucket> buckets = storage.list();
for (Bucket bucket : buckets.iterateAll()) {
  // do something with the info
}

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.
storage
  .getBuckets()
  .then((results) => {
    const buckets = results[0];

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

PHP

namespace Google\Cloud\Samples\Auth;

// Imports the Google 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

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

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