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apereo/cas

Open-source single sign-on and identity provider server in Java, supporting CAS, SAML2, OAuth2, OpenID Connect and multifactor authentication.

Open-source alternative to:OktaMicrosoft Entra IDAuth0

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What is it?

Apereo CAS is an enterprise identity provider and single sign-on server, so users sign in once and gain access to multiple applications. It began as the CAS protocol and this repository holds its main implementation, a Java server built on Spring Boot and Spring Cloud.

CAS supports CAS v1 to v3, SAML 2, OAuth 2.0, OpenID Connect and WS-Federation. It can authenticate against LDAP and Active Directory, relational databases, X.509 certificates, SPNEGO, RADIUS and other sources, and it can delegate login to external SAML2, OpenID Connect or social identity providers. Multifactor options include Duo Security, WebAuthn FIDO2, Google Authenticator and YubiKey.

Deployments can store tickets in Hazelcast, Redis, JPA or MongoDB, and run on embedded Tomcat or Jetty, in Docker or on Kubernetes. The project is maintained by the Apereo Foundation under Apache 2.0.

Key features

  • 01Supports CAS, SAML 2, OAuth 2.0, OpenID Connect and WS-Federation protocols
  • 02Authenticates against LDAP, Active Directory, databases, X.509 and RADIUS
  • 03Provides multifactor authentication including Duo, WebAuthn FIDO2 and YubiKey
  • 04Delegates login to external SAML2, OIDC and social identity providers
  • 05Stores tickets and service registries in Redis, JPA, MongoDB and other backends

Use cases

  • Providing one login page for a university or enterprise's internal web applications
  • Acting as a central SSO gateway that federates with external identity providers
  • Adding multifactor authentication to existing LDAP-backed user directories

Quick start

  1. 1

    Install Docker

  2. 2

    Start the official CAS image, replacing <version> with a tag from Docker Hub

    docker run --rm -p 8080:8080 -e SERVER_SSL_ENABLED=false -e SERVER_PORT=8080 apereo/cas:<version>
  3. 3

    Open http://localhost:8080/cas/login and log in as casuser with password Mellon

Things to know

  • Setting up a production server requires a configured WAR overlay and application registration, which takes effort.
  • The Docker quick start uses a demo login, so it is not a production configuration.

Topics

#authentication#sso#identity-provider#saml2#oauth2#openid-connect#mfa#spring-boot#authorization#aws

FAQ

What is cas?
Open-source single sign-on and identity provider server in Java, supporting CAS, SAML2, OAuth2, OpenID Connect and multifactor authentication. Apereo CAS is an enterprise identity provider and single sign-on server, so users sign in once and gain access to multiple applications. It began as the CAS protocol and this repository holds its main implementation, a Java server built on Spring Boot and Spring Cloud.
Is cas free to use? What license does it have?
cas is open source under the Apache-2.0 license. Check the license terms before using it in commercial products.
Is cas still maintained?
Actively maintained. The last commit to cas was on Oct 22, 2026.
What can I use cas for?
Providing one login page for a university or enterprise's internal web applications Acting as a central SSO gateway that federates with external identity providers Adding multifactor authentication to existing LDAP-backed user directories
How do I install cas?
Install Docker Start the official CAS image, replacing <version> with a tag from Docker Hub: docker run --rm -p 8080:8080 -e SERVER_SSL_ENABLED=false -e SERVER_PORT=8080 apereo/cas:<version> Open http://localhost:8080/cas/login and log in as casuser with password Mellon
Where can I get cas?
The source code and installation instructions are on GitHub: https://github.com/apereo/cas

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