Permissions required to authenticate to REST API

Hello,

One of our teams is requesting access to the Horizon 7.10 REST API to gather user session information and statistics.  I granted them Administrators(Read-only) role, but when trying to authenticate they get 

{

  "status": "UNAUTHORIZED",

  "timestamp": 1604401593260,

"error_message": "Only Administrator on Root are allowed to access the REST APIs."

}

Granting full Administrator access resolves this issue but I don't want them to have full Administrator permissions.  Does anyone know the minimum necessary permissions to authenticate to the REST API and gather user session data?

Thank you!