Authenticate calls to Google Cloud Functions programmatically - groovy

Question

I am trying to authenticate to Google Cloud Functions from SAP CPI to fetch some data from a database. To push data, we use pub/sub, with a service account access token, and it works perfectly. But for the functions, it needs an identity token instead of an access token. We get the previous token with a groovy script (No Jenkins). Is it possible to authenticate to the functions also with an access token? Or to get the identity token without building a whole IAP layer?

Answer 1

You have to call your Cloud Functions (or Cloud Run, it's the same) with a signed identity token.
So you can use a groovy script for generating a signed identity token. Here an example
import com.google.api.client.http.GenericUrl
import com.google.api.client.http.HttpRequest
import com.google.api.client.http.HttpRequestFactory
import com.google.api.client.http.HttpResponse
import com.google.api.client.http.javanet.NetHttpTransport
import com.google.auth.Credentials
import com.google.auth.http.HttpCredentialsAdapter
import com.google.auth.oauth2.IdTokenCredentials
import com.google.auth.oauth2.IdTokenProvider
import com.google.auth.oauth2.ServiceAccountCredentials
import com.google.common.base.Charsets
import com.google.common.io.CharStreams
String myUri = "YOUR_URL";
Credentials credentials = ServiceAccountCredentials
.fromStream(new FileInputStream(new File("YOUR_SERVICE_ACCOUNT_KEY_FILE"))).createScoped("https://www.googleapis.com/auth/cloud-platform");
String token = ((IdTokenProvider) credentials).idTokenWithAudience(myUri, Collections.EMPTY_LIST).getTokenValue();
System.out.println(token);
IdTokenCredentials idTokenCredentials = IdTokenCredentials.newBuilder()
.setIdTokenProvider((ServiceAccountCredentials) credentials)
.setTargetAudience(myUri).build();
HttpRequestFactory factory = new NetHttpTransport().createRequestFactory(new HttpCredentialsAdapter(idTokenCredentials));
HttpRequest request = factory.buildGetRequest(new GenericUrl(myUri));
HttpResponse httpResponse = request.execute();
System.out.println(CharStreams.toString(new InputStreamReader(httpResponse.getContent(), Charsets.UTF_8)));
Service account key file is required only if you are outside GCP. Else, the default service account is enough, but must be a service account. Your personal user account won't work
Add this dependency (here in Maven)
<dependency>
<groupId>com.google.auth</groupId>
<artifactId>google-auth-library-oauth2-http</artifactId>
<version>0.20.0</version>
</dependency>
Or you can use a tool that I wrote and open sourced. I also wrote a Medium article for explaining the use cases

Answer 2

You can only access your secured cloud function using Identity token.
1.Create a service account with roles/cloudfunctions.invoker
2.Create a cloud function that allows only authenticated requests
https://REGION-PROJECT_ID.cloudfunctions.net/FUNCTION_NAME
from google.oauth2 import service_account
from google.auth.transport.requests import AuthorizedSession
target_audience = 'https://REGION-PROJECT_ID.cloudfunctions.net/FUNCTION_NAME'
creds = service_account.IDTokenCredentials.from_service_account_file(
'/path/to/svc.json', target_audience=target_audience)
authed_session = AuthorizedSession(creds)
# make authenticated request and print the response, status_code
resp = authed_session.get(target_audience)
print(resp.status_code)
print(resp.text)