There are a few ways to grab your CustomerID from G Suite. This is important when configuring SSO or when interfacing with G Suite programmatically (through their lovely API).
The first and easiest way is to look at the web interface. This isn’t the most intuitive. To find the key, open Google Admin and then browse to Security in the menu in the upper left-hand corner, clicking on Dashboard.
Click on Single Sign On and then scroll down until you see EntityID. The EntityID is going to be everything after the = such as C034minsz9330 as follows
You can also find it by visiting the GooglePlay at https://play.google.com/work/adminsettings?pli=1 where it’s listed as Organization ID.
I don’t think this key can be changed. Once you have the key, you can communicate with the Google API Gateway. For example:
curl 'https://www.googleapis.com/admin/directory/v1/customers/$CUSTOMERKEY' \
--header 'Authorization: Bearer [$ACCESSTOKEN]' \
--header 'Accept: application/json' \
--compressed