Passing variable in asp to Crystal report Parameter field

I am using Crystal Reports 8.5 to design my reports and I am using enterprise 8 to view the reports. I view the report by simply typing in the name of the report into the browser address.

I have parameter fields that are prompted when the report first loads. Is there a way to pass my variables in asp to the parameter fields in Crystal reports?

ex:
var1 = session.variable("Logon_user")

Pass the value of var1 into the parameter field in Crystal reports called UserId.