Keycloak is an open source identity and access management solution that provides single sign-on for both legacy and new applications. It uses established standards like OAuth 2.0, OpenID Connect and SAML to securely authenticate users and manage authorization for multiple applications and services. Keycloak offers out-of-the-box features like social logins, user management, tokens and federation that make it easy to get started. It is also extensible through custom authentication mechanisms, event listeners and themes. Keycloak provides adapters to easily integrate with different frameworks and platforms.