Looking for sample Cisco CUBE configuration for SIP Proxy in "End-to-End Mode" using "Registrar Challenging the Register Request" Scenario

[ciscovoipsupport]

Hi Everyone,

I am looking for a sample configuration on Cisco CUBE acting as SIP Proxy. Specifically "End to End Mode" with "Registrar Challenging the Register Request" Scenario as shown below. 

EDIT: Objective is to not store any username or password for SIP account on the CUBE and everything needs to be provided by SIP Client.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/configuration/cube-book/voi-sip-reg-poxy.html

Has anyone tried this successfully?

I am using a CISCO2921 with SPA.155-3.M7.bin

I could get it to work in peer to peer mode. But failed to do in End to End mode. as i could not find any proper configuration on Cisco.com

Please assist.