Username & Digest Username (Authorization Username)

Hi all,

I am trying to interconnect OpenIMSCore with Asterisk as TAS.
I need to configure a SIP user with a different Authorization Username from Username.
I mean in X-lite:
Username: bob
Password: ***
Authorization Username:

How can i configure the sip.conf to get this?
The Authorization Username in X-lite is the Digest Username in SIP Header’s Authorization field.

Thanks in advance.