Linux SSO, Replicated Postfix Install & Configuration

Hello I need to provide SSO (linux users) to three VPSs with different providers and one Linux Server at my home which uses a local IP subnet (and access internet through the natted adsl router which has a static IP). In addition the SSO system needs to provide Web Users of various installed domains with authentication services. Need to implement a two way authentication using a permutation of Google Authenticator, Yubikey/Fido U2F & SMS/Twilio. Am thinking of using freeIPA as the SSO provider layer but am tied to it. Am open to suggestions. All I want is an integrated and web based management system. I am aware the web users will use SSO through their own Auth layer but I want ldap based SSO services to be provided through a higher layer so that every webapp does not have to do the base legwork everytime. One VPS will be primary for DNS, second will be primary for both, both will be secondary for each other, third will be primary for web applications. You have to provide one shot integration and guide us how to setup SSO for web applications.