How to pass parameter from Fusion to the VBCS application which is NOT embedded into Fusion?

Summary:

We have a PaaS VBCS application which we are trying to call from Fusion. Using sandbox (structure), we have created a new tile and added the static url of the VBCS app.

The VBCS application expects a parameter value from Fusion. Below is the VBCS app url (highlighted is the parameter that is expected by VBCS)

https://<vbcs-url>/ic/builder/rt/DSEJourney/1.0/webApps/dsejourney/?fusionusername

Please note: The VBCS app is not embedded in Fusion.

Please suggest, how do I get the Fusion username and pass it on the URL?

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