Proxy Authentication

Proxy authentication support for CAS v1+ protocols is enabled by default, thus it is entirely a matter of CAS client configuration to leverage proxy authentication features.

Disabling proxy authentication components is recommended for deployments that wish to strategically avoid proxy authentication as a matter of security policy.

Use Case

One of the more common use cases of proxy authentication is the ability to obtain a ticket for a back-end [REST-based] service that is also protected by CAS. The scenario usually is:

• User is faced with application A which is protected by CAS.
• Application A on the backend needs to contact a service S to produce data.
• Service S itself is protected by CAS itself.

Because A contacts service S via a server-to-service method where no browser is involved, service S would not be able to recognize that an SSO session already exists. In these cases, application A needs to exercise proxying in order to obtain a proxy ticket for service S. The proxy ticket is passed to the relevant endpoint of service S so it can retrieve and validate it via CAS and finally produce a response.

The trace route may look like this:

1. Browser navigates to A.
2. A redirects to CAS.
3. CAS authenticates and redirects back to A with an ST.
4. A attempts to validate the ST, and asks for a PGT.
5. CAS confirms ST validation, and issues a proxy-granting ticket PGT.
6. A asks CAS to produce a PT for service S, supplying the PGT in its request.
7. CAS produces a PT for service S.
8. A contacts the service S endpoint, passing along PT in the request.
9. Service S attempts to validate the PT via CAS.
10. CAS validates the PT and produces a successful response.
11. Service S receives the response, and produces data for A.
12. A receives and displays the data in the browser.

See the CAS Protocol for more info.

Handling SSL-enabled Proxy URLs

By default, CAS ships with a bundled HTTP client that is partly responsible to callback the URL for proxy authentication. Note that this URL need also be authorized by the CAS service registry before the callback can be made. See this guide for more info.

If the callback URL is authorized by the service registry, and if the endpoint is under HTTPS and protected by an SSL certificate, CAS will also attempt to verify the validity of the endpoint’s certificate before it can establish a successful connection. If the certificate is invalid, expired, missing a step in its chain, self-signed or otherwise, CAS will fail to execute the callback.

The HTTP client of CAS does present a local trust store that is similar to that of the Java platform. It is recommended that this trust store be used to handle the management of all certificates that need to be imported into the platform to allow CAS to execute the callback URL successfully. While by default, the local trust store to CAS is empty, CAS will still utilize both the default and the local trust store. The local trust store should only be used for CAS-related functionality of course, and the trust store file can be carried over across CAS and Java upgrades, and certainly managed by the source control system that should host all CAS configuration.

The following settings and properties are available from the CAS configuration catalog:

• Required
• Optional
• Signing & Encryption
• Hibernate & JDBC
• Email Servers
• LDAP & Active Directory
• Authentication
• Password Encoding
• Principal Transformation
• Password Policy
• Notes