How to Call WCF REST Cross Domain Securely using Jquery?

Hi Geeks 
I am using Jquery AJAX API for bi-directionally communicate with WCF REST Services  Cross-domain using  JsonP.
 Now, for my WCF REST service, I have used custom userNamePasswordValidationMode. how can i securely pass credentials in my jquery call to this wcf REST service. I dont want to use any library like oAuth  .Any help/pointers is appreciated :)
Thanks in Advance 
KP Singh Chundawat