disable user authentication for the clients consuming the web services hosted on Integration server

Integration server would challenge the web service consumer, and the apply ACL to check if the user got permissions to execute the service.

is there a way to disable the challenging bit of integration server for particular web service?

Ajay, what does ‘IS challenging web service consumer’ mean?

challenge - its general HTTP term. server (IS) is requesting the client to provide the authentication credentials

Yes, set the Execute ACL of the WSD to Anonymous.