Since I frequently look stuff like this up on the web, I decided to assemble a comprehensive Step-by-Step-Tutorial that you can follow to obtain an OAuth Client-ID to access Google’s APIs.
Open the Google Developers Console
Choose a name for your project
Click Create and wait for the project to be created
Once the little progress indicator in the upper right corner stopped spinning, click on it
Alternatively refresh your Dashboard to see the new project appear in the dropdown list at the top
In the left sidebar select APIs and Services
Under Dashboard you may add any API your project needs acces to
Select Credentials from the sidebar
Switch to the OAuth consent screen tab
Fill in the blanks and hit Save
You will be redirected to create your OAuth-Client-ID
Choose Web application and give it a name
Enter your domain for Authorized JavaScript origin
You will be prompted with your Client-ID as well as the key
Done.