Authentication#

Overview#

  • If you’re running in Compute Engine or App Engine, authentication should “just work”.

  • If you’re developing locally, the easiest way to authenticate is using the Google Cloud SDK:

    $ gcloud beta auth application-default login
    

    Note that this command generates credentials for client libraries. To authenticate the CLI itself, use:

    $ gcloud auth login
    

    Previously, gcloud auth login was used for both use cases. If your gcloud installation does not support the new command, please update it:

    $ gcloud components update
    
  • If you’re running your application elsewhere, you should download a service account JSON keyfile and point to it using an environment variable:

    $ export GOOGLE_APPLICATION_CREDENTIALS="/path/to/keyfile.json"
    

Client-Provided Authentication#

Every package uses a Client as a base for interacting with an API. For example:

from google.cloud import datastore
client = datastore.Client()

Passing no arguments at all will “just work” if you’ve followed the instructions in the Overview. The credentials are inferred from your local environment by using Google Application Default Credentials.

Credential Discovery Precedence#

When loading the Application Default Credentials, the library will check for credentials in your environment by following the precedence outlined by google.auth.default().

Explicit Credentials#

The Application Default Credentials discussed above can be useful if your code needs to run in many different environments or if you just don’t want authentication to be a focus in your code.

However, you may want to be explicit because

  • your code will only run in one place
  • you may have code which needs to be run as a specific service account every time (rather than with the locally inferred credentials)
  • you may want to use two separate accounts to simultaneously access data from different projects

In these situations, you can create an explicit Credentials object suited to your environment. After creation, you can pass it directly to a Client:

client = Client(credentials=credentials)

Google App Engine Environment#

To create credentials just for Google App Engine:

from google.auth import app_engine
credentials = app_engine.Credentials()

Google Compute Engine Environment#

To create credentials just for Google Compute Engine:

from google.auth import compute_engine
credentials = compute_engine.Credentials()

Service Accounts#

A service account is stored in a JSON keyfile.

The from_service_account_json() factory can be used to create a Client with service account credentials.

For example, with a JSON keyfile:

client = Client.from_service_account_json('/path/to/keyfile.json')

Tip

Previously the Google Cloud Console would issue a PKCS12/P12 key for your service account. This library does not support that key format. You can generate a new JSON key for the same service account from the console.

User Accounts (3-legged OAuth 2.0) with a refresh token#

The majority of cases are intended to authenticate machines or workers rather than actual user accounts. However, it’s also possible to call Google Cloud APIs with a user account via OAuth 2.0.

Tip

A production application should use a service account, but you may wish to use your own personal user account when first getting started with the google-cloud-python library.

The simplest way to use credentials from a user account is via Application Default Credentials using gcloud auth login (as mentioned above) and google.auth.default():

import google.auth

credentials, project = google.auth.default()

This will still follow the precedence described above, so be sure none of the other possible environments conflict with your user provided credentials.

Advanced users of oauth2client can also use custom flows to create credentials using client secrets or using a webserver flow. After creation, Credentials can be serialized with to_json() and stored in a file and then and deserialized with from_json(). In order to use oauth2client‘s credentials with this library, you’ll need to convert them.

Troubleshooting#

Setting up a Service Account#

If your application is not running on Google Compute Engine, you need a Google Developers Service Account.

  1. Visit the Google Developers Console.

  2. Create a new project or click on an existing project.

  3. Navigate to APIs & auth > APIs and enable the APIs that your application requires.

Note

You may need to enable billing in order to use these services.

  • BigQuery
    • BigQuery API
  • Datastore
    • Google Cloud Datastore API
  • Pub/Sub
    • Google Cloud Pub/Sub
  • Storage
    • Google Cloud Storage
    • Google Cloud Storage JSON API
  1. Navigate to APIs & auth > Credentials.

    You should see a screen like one of the following:

Find the “Add credentials” drop down and select “Service account” to be guided through downloading a new JSON keyfile.

If you want to re-use an existing service account, you can easily generate a new keyfile. Just select the account you wish to re-use, and click Generate new JSON key:

Using Google Compute Engine#

If your code is running on Google Compute Engine, using the inferred Google Application Default Credentials will be sufficient for retrieving credentials.

However, by default your credentials may not grant you access to the services you intend to use. Be sure when you set up the GCE instance, you add the correct scopes for the APIs you want to access:

  • All APIs

    • https://www.googleapis.com/auth/cloud-platform
    • https://www.googleapis.com/auth/cloud-platform.read-only
  • BigQuery

    • https://www.googleapis.com/auth/bigquery
    • https://www.googleapis.com/auth/bigquery.insertdata
  • Datastore

    • https://www.googleapis.com/auth/datastore
    • https://www.googleapis.com/auth/userinfo.email
  • Pub/Sub

    • https://www.googleapis.com/auth/pubsub
  • Storage

    • https://www.googleapis.com/auth/devstorage.full_control
    • https://www.googleapis.com/auth/devstorage.read_only
    • https://www.googleapis.com/auth/devstorage.read_write

Advanced Customization#

Warning

The developers of this library want to improve our HTTP handling to support more situations more easily, and use current tooling.

In order to allow this, this particular mechanism may have to be altered in a backwards-compatible way. Therefore, the following section should be considered “private API” that is subject to change.

The google-cloud-python library uses google-auth to sign requests and httplib2 for sending requests.

This is not a strict requirement: The Client constructor accepts an optional _http argument in place of a credentials object. If passed, all HTTP requests made by the client will use your custom HTTP object.

In order for this to be possible, the _http object must do two things:

The entire signature from httplib2 need not be implemented, we only use it as

http.request(uri, method=method_name, body=body, headers=headers)

For an example of such an implementation, a google-cloud-python user created a custom HTTP class using the requests library.

We hope to enable using custom HTTP libraries with this library at some point.