Authenticate for invocation

To invoke an authenticated Cloud Run function, the underlying principal must meet the following requirements:

• Have permission to invoke the function.
• Provide an ID token when it invokes the function.

What is a principal? As described in Secure your Cloud Run functions, Cloud Run functions supports two different kinds of identities, which are also called principals:

• Service accounts: These are special accounts that serve as the identity of a non-person, like a function or an application or a VM. They give you a way to authenticate these non-persons.
• User accounts: These accounts represent people, either as individual Google Account holders or as part of a Google-controlled entity like a Google Group.

See the IAM overview to learn more about basic IAM concepts.

To invoke an authenticated Cloud Run function, the principal must have the invoker IAM permission:

• run.routes.invoke. This is usually through the Cloud Run Invoker role. This permission must be assigned on the Cloud Run service resource.

To grant these permissions, use the add-invoker-policy-binding command, as shown in Authenticating function to function calls.

For permission to create, update, or perform other administrative actions on a function, the principal must have an appropriate role. Roles include permissions that define the actions that the principal is allowed to do. See Using IAM to Authorize Access for more information.

Invoking a function can have additional complexities. Event-driven functions can only be invoked by the event source to which they are subscribed, but HTTP functions can be invoked by different kinds of identities, originating in different places. The invoker might be a developer who is testing the function or another function or service that wishes to use the function. By default, these identities must provide an ID token with the request to authenticate themselves. In addition, the account being used must also have been granted the appropriate permissions.

Learn more about generating and using ID tokens.

Authentication examples

This section shows a few different examples of authenticating for invocation.

Example 1: Authenticate developer testing

As a developer, you need access to create, update, and delete functions, and this is granted using the normal (IAM) process.

But as a developer, you might need to invoke your functions for testing purposes. To invoke a function using curl or similar tools, note the following:

• Assign a role to your Cloud Run functions user account that contains the invoke permission.

  • run.routes.invoke. This is usually through the Cloud Run Invoker role.

• If you are working from your local machine, set up command-line access by initializing the Google Cloud CLI.

• Provide your request with authentication credentials as a Google-generated ID token stored in an Authorization header. For example, get an ID token using gcloud by running the following command:

  curl  -H "Authorization: Bearer $(gcloud auth print-identity-token)" \
    https://FUNCTION_URL
  

  where FUNCTION_URL is the URL of your function. Retrieve this URL from the Cloud Run functions page of the Google Cloud console or by running the gcloud functions describe command as shown in the first step of the Google Cloud CLI deployment command example.

You can use tokens created by gcloud to invoke HTTP functions in any project as long as your account has the cloudfunctions.functions.invoke permission on the function being invoked. For development purposes, use gcloud-generated ID tokens. However, note that such tokens lack an audience claim, which makes them susceptible to relay attacks. In production environments, use ID tokens issued for a service account with the appropriate audience specified. This approach enhances security by restricting token usage to the intended service only.

As always, we recommend that you allocate the minimum set of permissions required to develop and use your functions. Make sure that IAM policies on your functions are limited to the minimum number of users and service accounts.

Example 2: Authenticate function to function calls

When building services that connect multiple functions, it's a good idea to ensure that each function can only send requests to a specific subset of your other functions. For example, if you have a login function, it should be able to access the user profiles function, but it probably shouldn't be able to access the search function.

To configure the receiving function to accept requests from a specific calling function, you need to grant the appropriate invoker role to the calling function's service account on the receiving function. The invoker role is Cloud Run Invoker (roles/run.invoker) and must be granted on the underlying service:

gcloud functions add-invoker-policy-binding RECEIVING_FUNCTION \
  --member='serviceAccount:CALLING_FUNCTION_IDENTITY'

Because it will be invoking the receiving function, the calling function must also provide a Google-signed ID token to authenticate. This is a two step process:

1. Create a Google-signed ID token with the audience field (aud) set to the URL of the receiving function.

2. Include the ID token in an Authorization: Bearer ID_TOKEN header in the request to the function.

By far the easiest and most reliable way to manage this process is to use the authentication libraries, as shown below, to generate and employ this token.

Generate ID tokens

This section describes different ways you can generate the ID token a principal needs to invoke a function.

Unauthenticated access without an ID token is possible, but must be enabled. See Using IAM to Authorize Access for more information.

Generate tokens programmatically

After the following code generates an ID token, it calls your function with that token on your behalf. This code works in any environment where the libraries can obtain authentication credentials, including environments that support local Application Default Credentials.

/**
 * TODO(developer): Uncomment these variables before running the sample.
 */

// Cloud Functions uses your function's url as the `targetAudience` value
// const targetAudience = 'https://project-region-projectid.cloudfunctions.net/myFunction';
// For Cloud Functions, endpoint (`url`) and `targetAudience` should be equal
// const url = targetAudience;


const {GoogleAuth} = require('google-auth-library');
const auth = new GoogleAuth();

async function request() {
  console.info(`request ${url} with target audience ${targetAudience}`);
  const client = await auth.getIdTokenClient(targetAudience);

  // Alternatively, one can use `client.idTokenProvider.fetchIdToken`
  // to return the ID Token.
  const res = await client.request({url});
  console.info(res.data);
}

request().catch(err => {
  console.error(err.message);
  process.exitCode = 1;
});

import urllib

import google.auth.transport.requests
import google.oauth2.id_token


def make_authorized_get_request(endpoint, audience):
    """
    make_authorized_get_request makes a GET request to the specified HTTP endpoint
    by authenticating with the ID token obtained from the google-auth client library
    using the specified audience value.
    """

    # Cloud Functions uses your function's URL as the `audience` value
    # audience = https://project-region-projectid.cloudfunctions.net/myFunction
    # For Cloud Functions, `endpoint` and `audience` should be equal

    req = urllib.request.Request(endpoint)

    auth_req = google.auth.transport.requests.Request()
    id_token = google.oauth2.id_token.fetch_id_token(auth_req, audience)

    req.add_header("Authorization", f"Bearer {id_token}")
    response = urllib.request.urlopen(req)

    return response.read()

import (
	"context"
	"fmt"
	"io"

	"google.golang.org/api/idtoken"
)

// `makeGetRequest` makes a request to the provided `targetURL`
// with an authenticated client using audience `audience`.
func makeGetRequest(w io.Writer, targetURL string, audience string) error {
	// For Cloud Functions, endpoint (`serviceUrl`) and `audience` are the same.
	// Example `audience` value (Cloud Functions): https://<PROJECT>-<REGION>-<PROJECT_ID>.cloudfunctions.net/myFunction
	// (`targetURL` and `audience` will differ for GET parameters)
	ctx := context.Background()

	// client is a http.Client that automatically adds an "Authorization" header
	// to any requests made.
	client, err := idtoken.NewClient(ctx, audience)
	if err != nil {
		return fmt.Errorf("idtoken.NewClient: %w", err)
	}

	resp, err := client.Get(targetURL)
	if err != nil {
		return fmt.Errorf("client.Get: %w", err)
	}
	defer resp.Body.Close()
	if _, err := io.Copy(w, resp.Body); err != nil {
		return fmt.Errorf("io.Copy: %w", err)
	}

	return nil
}

import com.google.api.client.http.GenericUrl;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import com.google.auth.oauth2.IdTokenCredentials;
import com.google.auth.oauth2.IdTokenProvider;
import java.io.IOException;

public class Authentication {

  // makeGetRequest makes a GET request to the specified Cloud Run or
  // Cloud Functions endpoint `serviceUrl` (must be a complete URL), by
  // authenticating with an ID token retrieved from Application Default
  // Credentials using the specified `audience`.
  //
  // For Cloud Functions, endpoint (`serviceUrl`) and `audience` are the same.
  // Example `audience` value (Cloud Functions): https://project-region-projectid.cloudfunctions.net/myFunction
  public static HttpResponse makeGetRequest(String serviceUrl, String audience) throws IOException {
    GoogleCredentials credentials = GoogleCredentials.getApplicationDefault();
    if (!(credentials instanceof IdTokenProvider)) {
      throw new IllegalArgumentException("Credentials are not an instance of IdTokenProvider.");
    }
    IdTokenCredentials tokenCredential =
        IdTokenCredentials.newBuilder()
            .setIdTokenProvider((IdTokenProvider) credentials)
            .setTargetAudience(audience)
            .build();

    GenericUrl genericUrl = new GenericUrl(serviceUrl);
    HttpCredentialsAdapter adapter = new HttpCredentialsAdapter(tokenCredential);
    HttpTransport transport = new NetHttpTransport();
    HttpRequest request = transport.createRequestFactory(adapter).buildGetRequest(genericUrl);
    return request.execute();
  }
}

Generate tokens manually

If you're invoking a function and for some reason you cannot use the authentication libraries, there are two ways you can get the ID token manually, either using the Compute metadata server or by creating a self-signed JWT and exchanging it for a Google-signed ID token.

Use the metadata server

You can use the Compute metadata server to fetch ID tokens with a specific audience as follows:

curl "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/identity?audience=AUDIENCE" \
     -H "Metadata-Flavor: Google"

Replace AUDIENCE with the URL of the function you are invoking. You can retrieve this URL as described in the Authenticating developer testing section above.

Exchange a self-signed JWT for a Google-signed ID token

1. Grant the Invoker (roles/cloudfunctions.invoker) role to the calling function's service account on the receiving function.

2. Create a service account and a key and download the file with the private key (in JSON format) to the host from which the calling function or service makes its requests.

3. Create a JWT with the header set to {"alg":"RS256","typ":"JWT"}. The payload should include a target_audience claim set to the URL of the receiving function and iss and sub claims set to the email address of the service account used above. It should also include exp, and iat claims. The aud claim should be set to https://www.googleapis.com/oauth2/v4/token.

4. Use the private key downloaded above to sign the JWT.

5. Using this JWT, send a POST request to https://www.googleapis.com/oauth2/v4/token. Authentication data must be included in the header and the body of the request.

   In the header:

   Authorization: Bearer $JWT - where $JWT is the JWT you just created
   Content-Type: application/x-www-form-urlencoded
   

   In the body:

   grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer&assertion=$JWT
   

   Replace $JWT with the JWT you just created

   This returns another JWT which includes an id_token signed by Google.

Send your GET/POST request to the receiving function. Include the Google-signed ID token in an Authorization: Bearer ID_TOKEN_JWT header in the request.

What's next

• Learn how to manage access to functions.

• Get help with other ways to generate ID tokens.