Hi there! I am having a RESTful service to call via expression rule, for RE

Hi there!
I am having a RESTful service to call via expression rule, for REST service, as I know we can only use Authorization as opposed to Authentication in the header. So to pass the authorization parameter in the header, I am passing it like below and getting the correct response from the service however, for the userName and password, I should not pass these values directly so, I thought I could use the SCS field from the admin console to encrypt the username and password, but it is not working with encodebase64string() function.
Even the same thing I have tried with httpQuery smart service and got no luck in there as well. Any help on this topic would be highly appreciated!

headerValues: {"application/json","Basic " &"Basic " & encodebase64string("userName:password")}

OriginalPostID-184800

OriginalPostID-184800