Hello, how are you and welcome!
Answer:
C) OpenID Connect
Explanation:
The best option is OpenID Connect because is based in OAuth, and supports multiple web based and mobile clients, and supports REST.
With OAuth, we cannot make any user authentication just provide a token to access data.
RADIUS is a networking protocol, and Shibboleth is a single sign-on log-in system for computer networks and the Internet, both not support REST.
Restart the whole computer??
I think it is D because you would need there contact information in case something happens not there trade name
