I have created a CSE and need to programatically update the promotions. This is done in a backend system and user interaction in the authentication process is therefore not an option.

Updating the promotions can be done with their Custom Search API via HTTP. This process needs an authentication token.

Their documentation says that Custom Search only supports "ClientLogin" authentication. This has been deprecated by Google and it also involves CAPTCHAs so this is not an option. They also state that all authentication should be done through OAuth2 now.

**I have already implemented OAuth2 without user interaction with Google Analytics API.** 

My problem is:
**I cannot find the scope value for Custom Search API to use with OAuth2.** Any ideas?