EMA C++ Developers Guide : 6 Consuming Data from the Cloud : 6.4 Version 1 Authentication Using oAuth Password and Refresh_Token
 
6.4 Version 1 Authentication Using oAuth Password and Refresh_Token
6.4.1 Client_ID (AppKey) and Client Secret
To connect to Real-Time - Optimized infrastructure, the Enterprise Message API requires a Client_ID, and optionally can include a client secret. Client_IDs are generated using AppGenerator, which refers to the Client_ID as an AppKey. Each user must obtain their unique Client_ID using the machine account email sent by LSEG, which includes a link to AppGenerator. Keep your Client_ID private: do not share Client_IDs.
For further details on generating this ID, refer to the Real-Time - Optimized: Installation and Configuration for Client Use document. Each Client_ID is unique: do not share it with others.
For further details on supporting client secret submissions, refer to the Enterprise Message API C++ Edition Reference Manual.
For details on how OAuth uses a Client Secret with a Client ID and their relationship, refer to OAuth documentation at: the following URL: https://www.oauth.com/oauth2-servers/client-registration/client-id-secret/.