Which two options are requirements to use OAuth access tokens with Cisco Spark? (Choose two.)

A: Tokens must request access to servers before applications register to Cisco Spark. B: Servers must register to Cisco Spark as an application to request access tokens. C: Applications can only request the access token when the authenticated user grants permissions to this service D: Applications must register to Cisco Spark as a server to request access tokens. E: Services can request the access token only when the authenticated user grants permissions to this service.