V4 signing process with Cloud Storage tools

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V4 signing is a process you can use to generate signatures for authentication in Cloud Storage XML API requests. This page describes how to use gsutil and Cloud Storage client libraries to create signed URLs. Signed URLs give time-limited read or write access to a specific Cloud Storage resource. If you want to make your own program for creating signed URLs, read V4 signing with your own program instead.

Create a signed URL to download an object

To create a signed URL that can get an object from a bucket, complete the following steps:

gsutil

  1. Generate a new private key, or use an existing private key for a service account. The key can be in either JSON or PKCS12 format.

    For more information on private keys and service accounts, see Service Accounts.

  2. Use the gsutil signurl command, passing in the path to the private key from the previous step as well as the bucket and object name.

    For example, using a key stored in the folder Desktop, the following command generates a signed URL for users to view the object cat.jpeg for 10 minutes.

    gsutil signurl -d 10m Desktop/private-key.json gs://example-bucket/cat.jpeg

    If successful, your response should look like:

    URL    HTTP Method    Expiration    Signed URL
gs://example-bucket/cat.jpeg GET 2018-10-26 15:19:52 https://storage.googleapis.
com/example-bucket/cat.jpeg?x-goog-signature=2d2a6f5055eb004b8690b9479883292ae74
50cdc15f17d7f99bc49b916f9e7429106ed7e5858ae6b4ab0bbbdb1a8ccc364dad3a0da2caebd308
87a70c5b2569d089ceb8afbde3eed4dff5116f0db5483998c175980991fe899fbd2cd8cb813b0016
5e8d56e0a8aa7b3d7a12ee1baa8400611040f05b50a1a8eab5ba223fe5375747748de950ec7a4dc5
0f8382a6ffd49941c42498d7daa703d9a414d4475154d0e7edaa92d4f2507d92c1f7e811a7cab64d
f68b5df4857589259d8d0bdb5dc752bdf07bd162d98ff2924f2e4a26fa6b3cede73ad5333c47d146
a21c2ab2d97115986a12c28ff37346d6c2ca83e5618ec8ad95632710b489b75c35697d781c38e&
x-goog-algorithm=GOOG4-RSA-SHA256&x-goog-credential=example%40example-project.
iam.gserviceaccount.com%2F20181026%2Fus%2Fstorage%2Fgoog4_request&x-goog-date=
20201026T211942Z&x-goog-expires=3600&x-goog-signedheaders=host

    The signed URL is the string beginning with https://storage.googleapis.com and will likely extend for several lines. This URL can be used by any person to access the associated resource (in this case cat.jpeg) for the designated time frame (in this case, 10 minutes).

Client libraries

C++

For more information, see the Cloud Storage C++ API reference documentation. 

namespace gcs = ::google::cloud::storage;
using ::google::cloud::StatusOr;
[](gcs::Client client, std::string const& bucket_name,
   std::string const& object_name, std::string const& signing_account) {
  StatusOr<std::string> signed_url = client.CreateV4SignedUrl(
      "GET", std::move(bucket_name), std::move(object_name),
      gcs::SignedUrlDuration(std::chrono::minutes(15)),
      gcs::SigningAccount(signing_account));

  if (!signed_url) throw std::move(signed_url).status();
  std::cout << "The signed url is: " << *signed_url << "\n\n"
            << "You can use this URL with any user agent, for example:\n"
            << "curl '" << *signed_url << "'\n";
}

C#

For more information, see the Cloud Storage C# API reference documentation. 


using Google.Cloud.Storage.V1;
using System;
using System.Net.Http;

public class GenerateV4SignedReadUrlSample
{
    public string GenerateV4SignedReadUrl(
        string bucketName = "your-unique-bucket-name",
        string objectName = "your-object-name",
        string credentialFilePath = "my-local-path/my-credential-file-name")
    {
        UrlSigner urlSigner = UrlSigner.FromServiceAccountPath(credentialFilePath);
        // V4 is the default signing version.
        string url = urlSigner.Sign(bucketName, objectName, TimeSpan.FromHours(1), HttpMethod.Get);
        Console.WriteLine("Generated GET signed URL:");
        Console.WriteLine(url);
        Console.WriteLine("You can use this URL with any user agent, for example:");
        Console.WriteLine($"curl '{url}'");
        return url;
    }
}

Go

For more information, see the Cloud Storage Go API reference documentation. 

import (
	"context"
	"fmt"
	"io"
	"time"

	"cloud.google.com/go/storage"
)

// generateV4GetObjectSignedURL generates object signed URL with GET method.
func generateV4GetObjectSignedURL(w io.Writer, bucket, object string) (string, error) {
	// bucket := "bucket-name"
	// object := "object-name"

	ctx := context.Background()
	client, err := storage.NewClient(ctx)
	if err != nil {
		return "", fmt.Errorf("storage.NewClient: %v", err)
	}
	defer client.Close()

	// Signing a URL requires credentials authorized to sign a URL. You can pass
	// these in through SignedURLOptions with one of the following options:
	//    a. a Google service account private key, obtainable from the Google Developers Console
	//    b. a Google Access ID with iam.serviceAccounts.signBlob permissions
	//    c. a SignBytes function implementing custom signing.
	// In this example, none of these options are used, which means the SignedURL
	// function attempts to use the same authentication that was used to instantiate
	// the Storage client. This authentication must include a private key or have
	// iam.serviceAccounts.signBlob permissions.
	opts := &storage.SignedURLOptions{
		Scheme:  storage.SigningSchemeV4,
		Method:  "GET",
		Expires: time.Now().Add(15 * time.Minute),
	}

	u, err := client.Bucket(bucket).SignedURL(object, opts)
	if err != nil {
		return "", fmt.Errorf("Bucket(%q).SignedURL: %v", bucket, err)
	}

	fmt.Fprintln(w, "Generated GET signed URL:")
	fmt.Fprintf(w, "%q\n", u)
	fmt.Fprintln(w, "You can use this URL with any user agent, for example:")
	fmt.Fprintf(w, "curl %q\n", u)
	return u, nil
}

Java

For more information, see the Cloud Storage Java API reference documentation. 


import com.google.cloud.storage.BlobId;
import com.google.cloud.storage.BlobInfo;
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageException;
import com.google.cloud.storage.StorageOptions;
import java.net.URL;
import java.util.concurrent.TimeUnit;

public class GenerateV4GetObjectSignedUrl {
  /**
   * Signing a URL requires Credentials which implement ServiceAccountSigner. These can be set
   * explicitly using the Storage.SignUrlOption.signWith(ServiceAccountSigner) option. If you don't,
   * you could also pass a service account signer to StorageOptions, i.e.
   * StorageOptions().newBuilder().setCredentials(ServiceAccountSignerCredentials). In this example,
   * neither of these options are used, which means the following code only works when the
   * credentials are defined via the environment variable GOOGLE_APPLICATION_CREDENTIALS, and those
   * credentials are authorized to sign a URL. See the documentation for Storage.signUrl for more
   * details.
   */
  public static void generateV4GetObjectSignedUrl(
      String projectId, String bucketName, String objectName) throws StorageException {
    // String projectId = "my-project-id";
    // String bucketName = "my-bucket";
    // String objectName = "my-object";

    Storage storage = StorageOptions.newBuilder().setProjectId(projectId).build().getService();

    // Define resource
    BlobInfo blobInfo = BlobInfo.newBuilder(BlobId.of(bucketName, objectName)).build();

    URL url =
        storage.signUrl(blobInfo, 15, TimeUnit.MINUTES, Storage.SignUrlOption.withV4Signature());

    System.out.println("Generated GET signed URL:");
    System.out.println(url);
    System.out.println("You can use this URL with any user agent, for example:");
    System.out.println("curl '" + url + "'");
  }
}

Node.js

For more information, see the Cloud Storage Node.js API reference documentation. 

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 * Note: when creating a signed URL, unless running in a GCP environment,
 * a service account must be used for authorization.
 */
// The ID of your GCS bucket
// const bucketName = 'your-unique-bucket-name';

// The full path of your file inside the GCS bucket, e.g. 'yourFile.jpg' or 'folder1/folder2/yourFile.jpg'
// const fileName = 'your-file-name';

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

// Creates a client
const storage = new Storage();

async function generateV4ReadSignedUrl() {
  // These options will allow temporary read access to the file
  const options = {
    version: 'v4',
    action: 'read',
    expires: Date.now() + 15 * 60 * 1000, // 15 minutes
  };

  // Get a v4 signed URL for reading the file
  const [url] = await storage
    .bucket(bucketName)
    .file(fileName)
    .getSignedUrl(options);

  console.log('Generated GET signed URL:');
  console.log(url);
  console.log('You can use this URL with any user agent, for example:');
  console.log(`curl '${url}'`);
}

generateV4ReadSignedUrl().catch(console.error);

PHP

For more information, see the Cloud Storage PHP API reference documentation. 

use Google\Cloud\Storage\StorageClient;

/**
 * Generate a v4 signed URL for downloading an object.
 *
 * @param string $bucketName The name of your Cloud Storage bucket.
 *        (e.g. 'my-bucket')
 * @param string $objectName The name of your Cloud Storage object.
 *        (e.g. 'my-object')
 */
function get_object_v4_signed_url(string $bucketName, string $objectName): void
{
    $storage = new StorageClient();
    $bucket = $storage->bucket($bucketName);
    $object = $bucket->object($objectName);
    $url = $object->signedUrl(
        # This URL is valid for 15 minutes
        new \DateTime('15 min'),
        [
            'version' => 'v4',
        ]
    );

    print('Generated GET signed URL:' . PHP_EOL);
    print($url . PHP_EOL);
    print('You can use this URL with any user agent, for example:' . PHP_EOL);
    print('curl ' . $url . PHP_EOL);
}

Python

For more information, see the Cloud Storage Python API reference documentation. 

import datetime

from google.cloud import storage


def generate_download_signed_url_v4(bucket_name, blob_name):
    """Generates a v4 signed URL for downloading a blob.

    Note that this method requires a service account key file. You can not use
    this if you are using Application Default Credentials from Google Compute
    Engine or from the Google Cloud SDK.
    """
    # bucket_name = 'your-bucket-name'
    # blob_name = 'your-object-name'

    storage_client = storage.Client()
    bucket = storage_client.bucket(bucket_name)
    blob = bucket.blob(blob_name)

    url = blob.generate_signed_url(
        version="v4",
        # This URL is valid for 15 minutes
        expiration=datetime.timedelta(minutes=15),
        # Allow GET requests using this URL.
        method="GET",
    )

    print("Generated GET signed URL:")
    print(url)
    print("You can use this URL with any user agent, for example:")
    print(f"curl '{url}'")
    return url

Ruby

For more information, see the Cloud Storage Ruby API reference documentation. 

def generate_signed_url_v4 bucket_name:, file_name:
  # The ID of your GCS bucket
  # bucket_name = "your-unique-bucket-name"

  # The ID of your GCS object
  # file_name = "your-file-name"

  require "google/cloud/storage"

  storage = Google::Cloud::Storage.new
  storage_expiry_time = 5 * 60 # 5 minutes

  url = storage.signed_url bucket_name, file_name, method: "GET",
                           expires: storage_expiry_time, version: :v4

  puts "Generated GET signed url:"
  puts url
  puts "You can use this URL with any user agent, for example:"
  puts "curl #{url}"
end

Create a signed URL to upload an object

To create a signed URL that can upload an object to a bucket, complete the following steps:

gsutil

  1. Generate a new private key, or use an existing private key for a service account. The key can be in either JSON or PKCS12 format.

    For more information on private keys and service accounts, see Service Accounts.

  2. Use gcloud auth activate-service-account to authenticate with the service account:

    gcloud auth activate-service-account --key-file KEY_FILE_LOCATION/KEY_FILE_NAME

    Where:

  3. Use the gsutil signurl command with the -u option to reference the service account credentials.

    For example, the following command creates a signed url that allows users to upload an image file:

    gsutil signurl -m PUT -d 1h -c CONTENT_TYPE -u gs://BUCKET_NAME/OBJECT_NAME

    Where:

    • CONTENT_TYPE is the object's content type. For example, image/png.

    • BUCKET_NAME is the name of the bucket where the object is being uploaded. For example, example-bucket.

    • OBJECT_NAME is the name to assign to the uploaded object. For example, cat.png.

    If successful, your response should look like:

    URL    HTTP Method    Expiration    Signed URL
gs://example-bucket/cat.png PUT 2021-01-09 00:28:11 https://storage.googleapis.
com/example-bucket/cat.png?x-goog-signature=2d2a6f5055eb004b8690b9479883292ae74
50cdc15f17d7f99bc49b916f9e7429106ed7e5858ae6b4ab0bbbdb1a8ccc364dad3a0da2caebd308
87a70c5b2569d089ceb8afbde3eed4dff5086f0db5483998c175980991fe899fbd2cd8cb813b0016
5e8d56e0a8aa7b3d7215ee1baa8400611040f05b50a1a8eab5ba223fe1375747748de950ec7i6dc5
0f8382a6ffd4994ac42498d7daa703d9a414d4475154d0e7edaa92d4f2507d92c1f7e8efa7cab64d
f68b5df48575b9259d8d0bdb5dc752bdf07bd162d98ff2924f2p4a26fa6b3cede73ad5333c47d146
a21c2ab2d97b15986a12c68ff3734696c2ca83e56b8ec8ad95632710b488b75c35697d781c38e&
x-goog-algorithm=GOOG4-RSA-SHA256&x-goog-credential=example%40example-project.
iam.gserviceaccount.com%2F20181026%2Fus%2Fstorage%2Fgoog4_request&x-goog-date=
20201026T211942Z&x-goog-expires=3600&x-goog-signedheaders=host

    The signed URL is the string beginning with https://storage.googleapis.com and will likely extend for several lines. This URL can be used by any person to upload a resource (in this case cat.png) to the specified Cloud Storage bucket for the designated time frame (in this case, 1 hour).

Client libraries

C++

For more information, see the Cloud Storage C++ API reference documentation. 

namespace gcs = ::google::cloud::storage;
using ::google::cloud::StatusOr;
[](gcs::Client client, std::string const& bucket_name,
   std::string const& object_name, std::string const& signing_account) {
  StatusOr<std::string> signed_url = client.CreateV4SignedUrl(
      "PUT", std::move(bucket_name), std::move(object_name),
      gcs::SignedUrlDuration(std::chrono::minutes(15)),
      gcs::AddExtensionHeader("content-type", "application/octet-stream"),
      gcs::SigningAccount(signing_account));

  if (!signed_url) throw std::move(signed_url).status();
  std::cout << "The signed url is: " << *signed_url << "\n\n"
            << "You can use this URL with any user agent, for example:\n"
            << "curl -X PUT -H 'Content-Type: application/octet-stream'"
            << " --upload-file my-file '" << *signed_url << "'\n";
}

C#

For more information, see the Cloud Storage C# API reference documentation. 


using Google.Cloud.Storage.V1;
using System;
using System.Collections.Generic;
using System.Net.Http;

public class GenerateV4UploadSignedUrlSample
{
    public string GenerateV4UploadSignedUrl(
        string bucketName = "your-unique-bucket-name",
        string objectName = "your-object-name",
        string credentialFilePath = "my-local-path/my-credential-file-name")
    {
        UrlSigner urlSigner = UrlSigner.FromServiceAccountPath(credentialFilePath);

        var contentHeaders = new Dictionary<string, IEnumerable<string>>
        {
            { "Content-Type", new[] { "text/plain" } }
        };

        // V4 is the default signing version.
        UrlSigner.Options options = UrlSigner.Options.FromDuration(TimeSpan.FromHours(1));

        UrlSigner.RequestTemplate template = UrlSigner.RequestTemplate
            .FromBucket(bucketName)
            .WithObjectName(objectName)
            .WithHttpMethod(HttpMethod.Put)
            .WithContentHeaders(contentHeaders);

        string url = urlSigner.Sign(template, options);
        Console.WriteLine("Generated PUT signed URL:");
        Console.WriteLine(url);
        Console.WriteLine("You can use this URL with any user agent, for example:");
        Console.WriteLine($"curl -X PUT -H 'Content-Type: text/plain' --upload-file my-file '{url}'");
        return url;
    }
}

Go

For more information, see the Cloud Storage Go API reference documentation. 

import (
	"context"
	"fmt"
	"io"
	"time"

	"cloud.google.com/go/storage"
)

// generateV4GetObjectSignedURL generates object signed URL with PUT method.
func generateV4PutObjectSignedURL(w io.Writer, bucket, object string) (string, error) {
	// bucket := "bucket-name"
	// object := "object-name"

	ctx := context.Background()
	client, err := storage.NewClient(ctx)
	if err != nil {
		return "", fmt.Errorf("storage.NewClient: %v", err)
	}
	defer client.Close()

	// Signing a URL requires credentials authorized to sign a URL. You can pass
	// these in through SignedURLOptions with one of the following options:
	//    a. a Google service account private key, obtainable from the Google Developers Console
	//    b. a Google Access ID with iam.serviceAccounts.signBlob permissions
	//    c. a SignBytes function implementing custom signing.
	// In this example, none of these options are used, which means the SignedURL
	// function attempts to use the same authentication that was used to instantiate
	// the Storage client. This authentication must include a private key or have
	// iam.serviceAccounts.signBlob permissions.
	opts := &storage.SignedURLOptions{
		Scheme: storage.SigningSchemeV4,
		Method: "PUT",
		Headers: []string{
			"Content-Type:application/octet-stream",
		},
		Expires: time.Now().Add(15 * time.Minute),
	}

	u, err := client.Bucket(bucket).SignedURL(object, opts)
	if err != nil {
		return "", fmt.Errorf("Bucket(%q).SignedURL: %v", bucket, err)
	}

	fmt.Fprintln(w, "Generated PUT signed URL:")
	fmt.Fprintf(w, "%q\n", u)
	fmt.Fprintln(w, "You can use this URL with any user agent, for example:")
	fmt.Fprintf(w, "curl -X PUT -H 'Content-Type: application/octet-stream' --upload-file my-file %q\n", u)
	return u, nil
}

Java

For more information, see the Cloud Storage Java API reference documentation. 


import com.google.cloud.storage.BlobId;
import com.google.cloud.storage.BlobInfo;
import com.google.cloud.storage.HttpMethod;
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageException;
import com.google.cloud.storage.StorageOptions;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;

public class GenerateV4PutObjectSignedUrl {
  /**
   * Signing a URL requires Credentials which implement ServiceAccountSigner. These can be set
   * explicitly using the Storage.SignUrlOption.signWith(ServiceAccountSigner) option. If you don't,
   * you could also pass a service account signer to StorageOptions, i.e.
   * StorageOptions().newBuilder().setCredentials(ServiceAccountSignerCredentials). In this example,
   * neither of these options are used, which means the following code only works when the
   * credentials are defined via the environment variable GOOGLE_APPLICATION_CREDENTIALS, and those
   * credentials are authorized to sign a URL. See the documentation for Storage.signUrl for more
   * details.
   */
  public static void generateV4PutObjectSignedUrl(
      String projectId, String bucketName, String objectName) throws StorageException {
    // String projectId = "my-project-id";
    // String bucketName = "my-bucket";
    // String objectName = "my-object";

    Storage storage = StorageOptions.newBuilder().setProjectId(projectId).build().getService();

    // Define Resource
    BlobInfo blobInfo = BlobInfo.newBuilder(BlobId.of(bucketName, objectName)).build();

    // Generate Signed URL
    Map<String, String> extensionHeaders = new HashMap<>();
    extensionHeaders.put("Content-Type", "application/octet-stream");

    URL url =
        storage.signUrl(
            blobInfo,
            15,
            TimeUnit.MINUTES,
            Storage.SignUrlOption.httpMethod(HttpMethod.PUT),
            Storage.SignUrlOption.withExtHeaders(extensionHeaders),
            Storage.SignUrlOption.withV4Signature());

    System.out.println("Generated PUT signed URL:");
    System.out.println(url);
    System.out.println("You can use this URL with any user agent, for example:");
    System.out.println(
        "curl -X PUT -H 'Content-Type: application/octet-stream' --upload-file my-file '"
            + url
            + "'");
  }
}

Node.js

For more information, see the Cloud Storage Node.js API reference documentation. 

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 */
// The ID of your GCS bucket
// const bucketName = 'your-unique-bucket-name';

// The full path of your file inside the GCS bucket, e.g. 'yourFile.jpg' or 'folder1/folder2/yourFile.jpg'
// const fileName = 'your-file-name';

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

// Creates a client
const storage = new Storage();

async function generateV4UploadSignedUrl() {
  // These options will allow temporary uploading of the file with outgoing
  // Content-Type: application/octet-stream header.
  const options = {
    version: 'v4',
    action: 'write',
    expires: Date.now() + 15 * 60 * 1000, // 15 minutes
    contentType: 'application/octet-stream',
  };

  // Get a v4 signed URL for uploading file
  const [url] = await storage
    .bucket(bucketName)
    .file(fileName)
    .getSignedUrl(options);

  console.log('Generated PUT signed URL:');
  console.log(url);
  console.log('You can use this URL with any user agent, for example:');
  console.log(
    "curl -X PUT -H 'Content-Type: application/octet-stream' " +
      `--upload-file my-file '${url}'`
  );
}

generateV4UploadSignedUrl().catch(console.error);

PHP

For more information, see the Cloud Storage PHP API reference documentation. 

use Google\Cloud\Storage\StorageClient;

/**
 * Generate a v4 signed URL for uploading an object.
 *
 * @param string $bucketName The name of your Cloud Storage bucket.
 *        (e.g. 'my-bucket')
 * @param string $objectName The name of your Cloud Storage object.
 *        (e.g. 'my-object')
 */
function upload_object_v4_signed_url(string $bucketName, string $objectName): void
{
    $storage = new StorageClient();
    $bucket = $storage->bucket($bucketName);
    $object = $bucket->object($objectName);
    $url = $object->signedUrl(
        # This URL is valid for 15 minutes
        new \DateTime('15 min'),
        [
            'method' => 'PUT',
            'contentType' => 'application/octet-stream',
            'version' => 'v4',
        ]
    );

    print('Generated PUT signed URL:' . PHP_EOL);
    print($url . PHP_EOL);
    print('You can use this URL with any user agent, for example:' . PHP_EOL);
    print("curl -X PUT -H 'Content-Type: application/octet-stream' " .
        '--upload-file my-file ' . $url . PHP_EOL);
}

Python

For more information, see the Cloud Storage Python API reference documentation. 

import datetime

from google.cloud import storage


def generate_upload_signed_url_v4(bucket_name, blob_name):
    """Generates a v4 signed URL for uploading a blob using HTTP PUT.

    Note that this method requires a service account key file. You can not use
    this if you are using Application Default Credentials from Google Compute
    Engine or from the Google Cloud SDK.
    """
    # bucket_name = 'your-bucket-name'
    # blob_name = 'your-object-name'

    storage_client = storage.Client()
    bucket = storage_client.bucket(bucket_name)
    blob = bucket.blob(blob_name)

    url = blob.generate_signed_url(
        version="v4",
        # This URL is valid for 15 minutes
        expiration=datetime.timedelta(minutes=15),
        # Allow PUT requests using this URL.
        method="PUT",
        content_type="application/octet-stream",
    )

    print("Generated PUT signed URL:")
    print(url)
    print("You can use this URL with any user agent, for example:")
    print(
        "curl -X PUT -H 'Content-Type: application/octet-stream' "
        "--upload-file my-file '{}'".format(url)
    )
    return url

Ruby

For more information, see the Cloud Storage Ruby API reference documentation. 

def generate_upload_signed_url_v4 bucket_name:, file_name:
  # The ID of your GCS bucket
  # bucket_name = "your-unique-bucket-name"

  # The ID of your GCS object
  # file_name = "your-file-name"

  require "google/cloud/storage"

  storage = Google::Cloud::Storage.new
  storage_expiry_time = 5 * 60 # 5 minutes

  url = storage.signed_url bucket_name, file_name, method: "PUT",
                           expires: storage_expiry_time, version: :v4,
                           headers: { "Content-Type" => "text/plain" }
  puts "Generated PUT signed URL:"
  puts url
  puts "You can use this URL with any user agent, for example:"
  puts "curl -X PUT -H 'Content-Type: text/plain' --upload-file my-file '#{url}'"
end

What's next