Active Directory Federation Services (ADFS) is a crucial component for secure identity sharing among trusted partners, enabling users to access applications and services across organizational boundaries without the need to create multiple accounts. Although ADFS was primarily designed for Windows environments, the development of open-source tools and interoperability allows for configuring and managing this service on CentOS, a popular Linux distribution. This article focuses on the detailed process of installing, configuring, and managing ADFS on CentOS to ensure secure federated identity sharing.

System Preparation

Before initiating the installation, it is essential to ensure that the CentOS system is up to date and has all necessary dependencies installed. This step includes updating the system and installing key packages required for running ADFS.

sudo yum update -y
sudo yum install -y openldap-clients nss-tools openssl

Installation and Configuration of ADFS

ADFS is not directly available as a package for Linux, necessitating the use of compatible tools such as SAML2 or Shibboleth, which provide similar functionalities. For the purposes of this guide, we will use Shibboleth, which is freely available and widely supported.

1. Installation of Shibboleth

   Shibboleth can be installed directly from CentOS repositories:

   sudo yum install -y shibboleth
   

2. Shibboleth Configuration

   After installation, it is necessary to configure Shibboleth for operation with ADFS. This step involves editing Shibboleth configuration files located in /etc/shibboleth/, where parameters for communicating with the ADFS server need to be set.

   In the shibboleth2.xml configuration file, it is necessary to set the entityID of your organization and metadata of the Identity Provider (IdP), which in our case will be the ADFS server. Additionally, configure the Assertion Consumer Service (ACS) URL, which is used for receiving identity assertions from ADFS.

3. Establishing Trusted Communication

   Trusted communication between Shibboleth and ADFS requires mutual sharing of certificates. On the ADFS side, export the certificate and subsequently import it into the Shibboleth keystore, typically located in /etc/shibboleth/.

4. ADFS Configuration

   On the ADFS side, create a new relying party trust for Shibboleth, which involves importing Shibboleth metadata into ADFS and configuring rules for issuing claims. This configuration enables ADFS to recognize requests coming from Shibboleth and respond accordingly.

Testing and Debugging

After completing the configuration, it is crucial to perform testing of the entire solution to ensure that federated authentication works correctly and securely. Testing involves verifying communication between Shibboleth and ADFS, proper issuance and acceptance of identity claims, and also checking security aspects of the entire process.

1. Communication Verification

   Start by verifying basic communication between Shibboleth and ADFS using tools like curl or wget. The goal is to check if both services can communicate with each other and exchange metadata.

   curl -k https://<adfs-server>/FederationMetadata/2007-06/FederationMetadata.xml
   

   This command should return metadata of the ADFS server, indicating that basic communication is functional.

2. Authentication Testing

   Next, perform a user authentication test through Shibboleth, observing whether the user is successfully redirected to ADFS for login and returns back to the application with valid identity assertions after authentication.

3. Debugging

   In case of authentication issues or assertion exchange problems, debugging configuration may be necessary. Utilize Shibboleth and ADFS logs, typically found in /var/log/shibboleth/ and Windows Event Viewer respectively, to identify and address issues

Maintenance and Updates

Proper maintenance and regular updates are crucial to ensure the security and stability of the federative service. This includes not only updating CentOS and Shibboleth but also monitoring for new versions of ADFS and applying security patches as necessary.

1. Regular Updates

   Keep track of releases for Shibboleth, CentOS, and ADFS, and regularly perform updates to keep your systems protected against security threats.

2. Monitoring and Auditing

   Implement monitoring and auditing solutions to track activities related to federated identity sharing and promptly respond to any security incidents.

Federated authentication and identity sharing among trusted partners offer organizations flexibility and increased security when accessing applications and services. With tools like Shibboleth and proper configuration, these benefits can be fully realized even in CentOS environments. However, it is crucial not to underestimate the requirements for proper installation, configuration, and especially ongoing maintenance and updates to ensure the security and reliability of systems.