I need to read/insert events into a specific calendar, using Google API. All registered users (in my app) can read and insert events into the calendar. I don't have to authenticate each user with OAuth 2.0, because the app will not read the user data - only specific account data.
I'm a professor and all my students can read and insert in my calendar. So, they do not need to login (Google Account) to do it, because it's a single account's data.
Is there a way to set a unique key for the main account?
OAuth2 doesn't makes me sense.
Maybe you need a service account here. It is an account that belongs to your application instead of to an individual end-user. Your application calls Google APIs on behalf of the service account, and user consent is not required. (In non-service-account scenarios, your application calls Google APIs on behalf of end-users, and user consent is sometimes required.)
The Calendar API can use the Delegating domain-wide authority to the service account. For example, an application that uses the Google Calendar API to add events to the calendars of all users in a Google Apps domain would use a service account to access the Google Calendar API on behalf of users.
For more information, check these threads: