How to set credentials for all teststeps at testcase level

Hi,

I have a list of teststeps under a testcase. I need to set the credentials(username/password) at the testcase level.I do have a option in SOAPUI GUI to set the credentials at testcase level and it applies to all teststeps in the testcase but my requirement is to set the credentials(username/password) at the testcase level using Groovy script to make it dynamic at runtime to pick the username/password from the external source.

Could you please give us the list of SOAPUI API's and the way to achieve the result.

Thanks,
Senthil Kumar S