I'm trying to access the Google Cloud API from an AWS Lambda function but I don't know how to authenticate. The auth guide in the Google Cloud documentation (https://cloud.google.com/docs/authentication) wants me to download a credentials JSON file and use Application Default Credentials, but as anyone who has used hosted functions already knows, the point is that you don't need to manage a server or runtime environment, so Lambda doesn't give me the ability to store arbitrary files in the environment of the running code.
I can use the Cloud SDK locally to get an access token but it expires so I can't use it in my function as a permanent solution.
Is there not a way I can get an access token that I can use indefinitely in my code to call the Google Cloud API? Is there any other solution?