Hello,
I solved the problem by few steps:
1) in IIS Default Web Sitesy\OpcenterRDnLGIL\ allow Basic authentification.
2) Switch from Mendix Studio Pro 9.6.1 to Mendix Studio Pro 9.21.0.
3) Choose a template with Mendix SSO (Asset Manager template from Mendix Studio).
4) in connection settings of the Consumed Odata service set up 'MyUser' and 'MyPass'.
Instead of writing
IF 1 < 2 THEN 'MyUserName' else 'MyUserName2'
you can also write
'MyUserName'
If you click the 'help' button (question mark) at the bottom of the dialog, a browser tab opens on https://docs.mendix.com/refguide/expressions/, which explains more about expressions.