If your plan is to develop a tool or desktop app instead of a server-side application, the benefits of application default credentials are less obvious and reusing the user’s personal gcloud credentials instead might seem attractive. But there are some pitfalls.
gcloud manages two sets of credentials, your personal credentials and application default credentials. Having two separate credentials might seem redundant and can cause surprises the first time you use one of the Google Cloud client libraries. But the two credentials serve different purposes.
Google APIs use OAuth 2.0 for authentication and authorization. To call an API, you first have to obtain an access token for the right scope and then pass it to the respective API by using the
Authorization HTTP header.
But the trouble with access tokens is that they are short-lived, and you somehow have to deal with expiring tokens…
Once you’ve signed in on google.com, the Cloud Console, or any other Google site, your browser session remains valid for multiple days. Not being prompted to sign in over and over again is convenient and at least in typical consumer scenarios, the risk that comes along with keeping the session is limited.
Things can look different in a corporate scenario where users might have access to sensitive data. Keeping sessions alive for 14 days (which is the default) might seem a little risky and might not be in line with an enterprise’s idea of security. G Suite Business and Cloud Identity Premium therefore allow you to change the default session length to a different period such as 8 hours. This setting applies to all Google services, not only GCP.
Recently, Google introduced another way to control session lifetime by allowing you to control the session length for Cloud Console and gcloud sessions.