RD Web without authentication prompt

Hi,

I've a RD Web configured on my new Server 2019.

This is my situation: I've 50 users pre-configured on my server and enabled to connect via RDWeb (all RDS CALs are active).

My request: through a specific web app a visitor clicks on "start an RDP session". Now the web app select one pre-configured user and makes the authentication automatically without asking username and password to the visitor but setting these parameters by it self.

Is it possible to set a connection parameter to specify username and password to use for RDWeb connection?

Is there another method to achieve this goal?

Thank you.