[keycloak-user] Get Keycloak to include AttributeConsumingServiceIndex in SAML2.0 AuthnRequest

We are using Keycloak as identity federation gateway, and one of the IdPs we are trying to connect to requires that SAML requests specify a AttributeConsumingServiceIndex so that the desired requested attributed can be returned. Have not been able to find a way to specify the index vlue so that the AttributeConsumingServiceIndex can be included in the request as part of configuring a SAML provider under Identity Providers. Any recommendations on how to configure this? Thanks, -Georgi