Most of the operations you perform in Cloud Storage must be authenticated.
The only exceptions are operations on objects that allow anonymous
access. Objects are anonymously accessible if the
READ permission. The
allUsers group includes
anyone on the Internet.
Cloud Storage uses OAuth 2.0 for API authentication and authorization. Authentication is the process of determining the identity of a client. The details of authentication vary depending on how you are accessing Cloud Storage, but fall into two general types:
A server-centric flow allows an application to directly hold the credentials of a service account to complete authentication. Use this flow if your application works with its own data rather than user data. Google Cloud Platform projects have default service accounts you can use, or you can create new ones.
A user-centric flow allows an application to obtain credentials from an end user. The user signs in to complete authentication. Use this flow if your application needs to access user data. See the User account credentials section later in this page for scenarios where a user-centric flow is appropriate.
Keep in mind that you can use both types of authentication together in an application. For more background information about authentication, see the Google Cloud Platform Auth Guide.
Authorization is the process of determining what permissions an authenticated
identity has on a set of specified resources. OAuth uses scopes to
determine if an authenticated identity is authorized. Applications use a
credential (obtained from a user-centric or server-centric authentication flow)
together with one or more scopes to request an access token from a Google
authorization server to access protected resources. For example, application A
with an access token with
read-only scope can only read, while application B
with an access token with
read-write scope can read and modify data. Neither
application can read or modify access control lists on objects and buckets;
only an application with
full-control scope can do so.
||Only allows access to read data, including listing buckets.||
||Allows access to read and change data, but not metadata like IAM policies.||
||Allows full control over data, including the ability to modify IAM policies.||
||View your data across Google Cloud Platform services. For Cloud Storage,
this is the same as
||View and manage data across all Google Cloud Platform services. For
Cloud Storage, this is the same as
Use an existing service account or create a new one, and download the associated private key.
gcloud auth activate-service-accountto authenticate with the service account:
gcloud auth activate-service-account --key-file [KEY_FILE]
Where [KEY_FILE] is the name of the file that contains your service account credentials.
gcloud auth uses the
cloud-platform scope when getting an
If you installed gsutil independent of the Cloud SDK, then see the gsutil install page for information about how to authenticate.
Client library authentication
Client libraries can use Application Default Credentials to easily authenticate with Google APIs and send requests to those APIs. With Application Default Credentials, you can test your application locally and deploy it without changing the underlying code. For more information, including code samples, see Google Cloud Platform Auth Guide.
Google Cloud Platform
If you're running your application on App Engine or Compute Engine, the environment already provides a service account's authentication information, so no further setup is required. For Compute Engine, the service account scope depends on how you created the instance. See Setting the scope of service account access for instances. For App Engine, the
cloud-platformscope is used.
To initialize your local development or production environment, create a GCP service account, download its key, and set the
GOOGLE_APPLICATION_CREDENTIALSenvironment variable to use the key. For step-by-step information, see Setting up authentication with Cloud Storage client libraries. As an alternative to setting an environment variable, you can also use the service account key directly in code.
Authorization: Bearer <oauth2_token>
The following is an example of a request that lists objects in a bucket.
Use the list method of the Objects resource.
GET /storage/v1/b/example-bucket/o HTTP/1.1 Host: www.googleapis.com Authorization: Bearer ya29.AHES6ZRVmB7fkLtd1XTmq6mo0S1wqZZi3-Lh_s-6Uw7p8vtgSwg
Use a List objects request.
GET / HTTP/1.1 Host: example-bucket.storage.googleapis.com Authorization: Bearer ya29.AHES6ZRVmB7fkLtd1XTmq6mo0S1wqZZi3-Lh_s-6Uw7p8vtgSwg
Due to the complexity of managing and refreshing access tokens and the security risk when dealing directly with cryptographic applications, we strongly encourage you to use a verified client library.
If you're looking for developer keys to use with the XML API for interoperable access with Amazon S3, see Managing developer keys for a simple migration.
User account credentials
Use user account credentials for authentication when your application requires access to data on a user's behalf; otherwise, use service account credentials. Here are examples of scenarios where user account credentials can be used:
- Web server applications
- Installed and desktop applications
- Mobile applications
- Applications on limited-input devices
For more information on these scenarios, see OAuth scenarios.
If you are designing an application to support multiple authentication options for end users, then use Firebase Authentication, which supports email and password authentication as well as federated sign in with identity providers such as Google, Facebook, Twitter, and GitHub.
When an application is granted an access token in a user-centric auth flow by
an end-user, that access token will only have the permissions available to the
user who grants the token. For example, if email@example.com has
example-bucket, an application which Jane has granted
to will be unable to write to
example-bucket on her behalf.
- Learn about browser-based downloads using cookie authentication.
- Learn about how service accounts are used generally in Google Cloud Platform and specifically in Cloud Storage