Adding GoogleDrive to your ownCloud deployment is a tricky job, so it is complex to complete and undocumented. Simply following ownCloud guide won't make you get the job done, (this is my personal experience) as there are steps missing.
So, here is my guide personalized for the Pennyitsupport cloud built on the ownCloud generic server. You may already have completed some steps as you will go through, yet, I advise to follow the steps and create new projects from scratch. Let's start now:
Sign in to https://console.developers.google.com/#identifier with your google account:
Click on Drive API in the Google Apps APIs section:
Click on Create project:
Choose a name or leave the default, chose to get updated or not and agree on terms and conditions, then click on Create:
Once created, Enable the project:
After enabling the project, you get an information screen instructing for credentials creation:
Click on Go to Credentials:
Click Create client ID to create the ID:
Setup the OAuth 2.0 client screen. Leve the Email address set by default and fill in the Product name shown to users: Pennyitsupport or the name of your choice then click Continue:
Credentials are created:
You can download and save the credentials, then click Done. Note that downloaded credentials are a kind of xml format and retrieve credentials in the file may be tricky. You don't need to download them as you can retrieve them online.
Now, you have successfully created the Google Drive Client API.
If you are a regular user, skip this step and go to the Pennyitsupport cloud sign in step.
For domain owners, before allowing ownCloud to connect to GoogleDrive through the created client, administrator must go through the Domain verification. My personal experience shows that I was unable to add GoogleDrive to ownCloud until I went through the Domain verification. So, click on Domain verification:
Click Add domain: