In this talk, i will deliver my experiences as part of engineering team who build Single Sign On Services (SSO) using F/OSS. This talk will cover two kinds of implementation which my team and I has been done during these six years journey. The first implementation is based on Central Authentication Services ( CAS ) at University of Indonesia (UI). By using CAS mechanism, we integrate separate authentication system on UI internal apps to a Centralized Identity Provider. Besides that, we are using it for UI Infrastructure Services, such as WiFI Access and Laboratory Internet Access. We also provide single authentication for external services which UI also subscribed , such as Google Apps for Education and Office365. The second implementation is based on OAuth at Peentar. Peentar is an emerged startup on Indonesia on Internet of Things and Integrated Omni channel Platform. I am a part of co-founding team since 2015. As a platform based provider, we need to allow user to authenticate on our platform using multiple resources provider. OAuth protocol enables us to do so. All of these implementation are build using F/OSS . CAS is implemented using JASIG CAS (https://github.com/apereo/cas). OAuth Stack is implemented using Hydra (https://github.com/ory/hydra) and our own ConsentApps.