To access a user's Google Drive on their behalf without relying on the user's credentials and following Google-recommended practices, you should use a service account with domain-wide delegation.

Create a Service Account:

Go to the Cloud Console, navigate to IAM & Admin > Service Accounts.

Click "Create Service Account" and provide necessary details.

Grant Domain-Wide Delegation:

Edit the service account to enable "G Suite Domain-wide Delegation".

Download the JSON key file.

Configure API Access in G Suite:

Go to the Google Admin Console.

Navigate to Security > API Controls > Domain-wide Delegation.

Add a new API client and use the client ID from the service account.

Authorize the necessary API scopes (e.g., https://www.googleapis.com/auth/drive).

Implement in Application:

Use the Google API Client Library for the desired language.

Load the service account credentials and perform user impersonation to access Google Drive.

Domain-wide Delegation of Authority

Using OAuth 2.0 for Server to Server Applications