LemonLDAP::NG is an open source software that provides single sign-on and identity federation capabilities. It allows users to authenticate once and access multiple applications securely. It supports standards like CAS, SAML and OpenID Connect for authentication. LemonLDAP::NG also provides ways to protect APIs and web services using tokens validated by handlers. It has been an OW2 project since 2003 and supports protocols for federation between identity providers.