A is incorrect: 'No Authentication' is unsuitable for secure APIs requiring an Entra ID token, as it would not provide the necessary credential. Passing `user.id` alone is not an authentication method for a secure API.
B is incorrect: 'Only for Teams' provides basic user identity from Teams but does not facilitate the acquisition of a full Entra ID authentication token necessary for secure, external REST API calls.
C is correct: To interact with a secure external API that requires a user's Entra ID token, the bot must acquire an OAuth token on behalf of the user. 'Authenticate manually' with Entra ID allows for this. Configuring SSO in Teams ensures the bot can silently obtain this token without repeatedly prompting the user to log in.
D is incorrect: Hardcoding a Service Principal client secret directly into the bot is a security risk and typically used for application-level authentication, not for authenticating as the end-user to acquire their specific data from an external API.