Click in the upper left part to see a sliding sidebar. Next, click API Manager. In the list of APIs look for Calendar API and make sure it is enabled ( If its not enable then enable it first ).
In the sidebar on the left, select Credentials.
Go to OAuth consent screen tab and give a name to the product, then click Save.
Go to Credentials tab and in New credentials drop-down menu select OAuth client ID.
Select Web application and create your project's OAuth 2.0 credentials by providing the necessary information. For Authorized redirect URIs enter the Redirect URI found below on this page. Click Create.
In the popup window look for the Client ID and Client secret. Use them in the form below on this page.
Save Settings and click Verify Account which is located at the bottom of this page.
