In our project we are making use an IDP that acts as a broker for us to multiple IDP's. The communication is based on the SAML v2 specification. Through the broker we are using 3 different IDP's to login to our application. To connect to the broker we have setup an authentication service. 

In our application we have 2 external portals. 1 portal should always go to 1 IDP of the broker while the other portal should come up with a screen (provided by the broker) where the user can select the desired IDP (out of the 3 options).

Our broker informed us that this requirement is possible. It can be achieved by providing the desired IDP in the AuthnRequest to them. The SAML specification provides a xml tag Scoping to hold this information. See below screenshot:

The problem is that from the Authentication service I am not able to configure the information. 

I did find this community page https://support.pega.com/question/extending-saml-v2-metadata-pega-74. However I do not see an option for my requirement to extend this activity. 

Can anyone help me with this requirement? Or is this a product enhancement.