How to bind to current riacontext user in xaml

I Have a datacontext that has a "getuserbyguid" method, i want to pass in the current logged in user.userid as a parameter, but I don't know how to bind to the current logged in user through xaml. I've tried {Binding Path=User.UserId} but without any luck. I'm using the built in riaservices authentication methods, so the userinfo should be exposed in the riacontext, or am I wrong about this?

I have this for instance

<riaControls:DomainDataSource x:Name="FollowingGridData" AutoLoad="True" QueryName="GetUsersFollowedByIDQuery" LoadSize="20">
        <riaControls:DomainDataSource.DomainContext>
            <my:NotesDomainContext />
        </riaControls:DomainDataSource.DomainContext>
        <riaControls:DomainDataSource.QueryParameters>
            <riaControls:Parameter ParameterName="userguid" Value="{Binding Path=User.UserId}" />
        </riaControls:DomainDataSource.QueryParameters>
    </riaControls:DomainDataSource>

But it gives me an error saying that开发者_JAVA百科 it's not a guid, meaning that it must not be binding correctly

The correct binding was

{Binding Source={StaticResource WebContext}, Path=User.DisplayName}