How can curl authenticate to Google Cloud based on local gcloud's CLI authentication? - authentication

Question

My script uses a sequence of gcloud commands and of course gcloud is authenticated. I need to use curl to access GCP REST APIs that are not available to gcloud. I can do this by generating a JSON credentials file in the Cloud Console, but I'd rather not do that as a separate manual step.
[Edit: The answer is to replace the gcloud auth string in that curl command with gcloud auth print-access-token. See answer below.]
This is how I do it now, using a JSON file downloaded from the Console.
GOOGLE_APPLICATION_CREDENTIALS=credentials.json
curl -X POST -H "Authorization: Bearer \"$(gcloud auth application-default print-access-token)\"" \
-H "Content-Type: application/json; charset=utf-8" \
https://cloudresourcemanager.googleapis.com/v1/projects/<MY_PROJECT>:getAncestry
Without that downloaded JSON, I get this:
ERROR: (gcloud.auth.application-default.print-access-token)
The Application Default Credentials are not available. They are available if running in Google Compute Engine.
Otherwise, the environment variable GOOGLE_APPLICATION_CREDENTIALS must be defined pointing
to a file defining the credentials. See https://developers.google.com/accounts/docs/application-default-credentials
for more information.
{ "error": {
"code": 401,
"message": "Request had invalid authentication credentials.
Expected OAuth 2 access token, login cookie or other valid authentication credential.
See https://developers.google.com/identity/sign-in/web/devconsole-project.",
"status": "UNAUTHENTICATED"
}
}
How can I leverage my gcloud authentication to use curl? I don't mind using the JSON if I can automate its generation as part of this script. For example, is there a way to call gcloud to generate this JSON, which I would then set as GOOGLE_APPLICATION_CREDENTIALS?

Answer 1

Once you have the Cloud SDK authenticated, you can use the gcloud auth print-access-token command to get an access token for the current active account, without the need of specifying the path to the JSON credentials file.
You will still need the credentials.json file, if you wish to activate a service account for the Cloud SDK instance. However, I am pretty sure you will only have to do that once.
EDIT:
I noticed you are using the gcloud auth application-default print-access-token.
Keep in mind that, contrary to the gcloud auth print-access-token command, it uses the current Application Default Credential (ADC), which has to be set by specifying the credentials.json file path with the GOOGLE_APPLICATION_CREDENTIALS env variable, or by using the gcloud auth application-default login command.