Which role would you need to grant to an existing user for them to manage...

To manage Controller security settings, you would need to grant the Security Administrator role to an existing user. The Security Administrator role is a built-in role that allows the user to access and modify the security settings of the Controller, such as encryption, certificates, authentication, authorization, and audit1. The Security Administrator role also inherits the permissions of the Credentials Administrator role, which allows the user to manage the credentials for the Controller and the agents2. The other roles listed do not have the permission to manage Controller security settings. The Administrator role can perform most administrative tasks, but not security-related ones2. The Analytics Administrator role can manage the analytics platform and data, but not theController security3. The Account Owner role can manage the account settings and licenses, but not the Controller security4

https://docs.appdynamics.com/appd/21.x/21.1/en/application-monitoring/install-app-server-agents/agent-to-controller-connections