Gmail

Google documentation provides latest details for enabling API access via a service account here

Access the Google cloud console here

• Select the appropriate project
• Click on IAM & Admin
• Click on Service Accounts
• Click on +Create Service Account
  • Enter a name and description for the service account
  • Click create and continue
  • Select a role, search for and select Identity Toolkit Viewer
  • Click Done
• Click on the newly created service account
  • Click keys
  • Add Key-Create New Key
  • Select json - create
  • Save the json to disk

Access the Google Admin console here

• Expand Security
• Expand Access and data control
• Click on API Controls
• Click on Manage Domain Wide Delegation
• Under API Clients click Add new
  • Paste in the Unique ID of the service account created in previous section
  • Paste the following list of Oath scopes and click Authorize

https://www.googleapis.com/auth/admin.directory.group.readonly,https://www.googleapis.com/auth/cloud-identity.policies,https://www.googleapis.com/auth/admin.directory.user.readonly,https://www.googleapis.com/auth/admin.directory.orgunit.readonly

Access the Prelude SCM Integration page here

• Click add integration
• Select Gmail
• Name the integration
• Enter Gmail administrator email address
• Browse to upload the json from previous step
• Click connect