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.

:information_source: Service Configuration

Note that each registered application in the registry must explicitly be configured to allow for proxy authentication. See this guide to learn about registering services in the registry.

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:

The configuration settings listed below are tagged as Required in the CAS configuration metadata. This flag indicates that the presence of the setting may be needed to activate or affect the behavior of the CAS feature and generally should be reviewed, possibly owned and adjusted. If the setting is assigned a default value, you do not need to strictly put the setting in your copy of the configuration, but should review it nonetheless to make sure it matches your deployment expectations.

The configuration settings listed below are tagged as Optional in the CAS configuration metadata. This flag indicates that the presence of the setting is not immediately necessary in the end-user CAS configuration, because a default value is assigned or the activation of the feature is not conditionally controlled by the setting value. In other words, you should only include this field in your configuration if you need to modify the default value or if you need to turn on the feature controlled by the setting.

  • cas.http-client.allow-local-urls=false
  • Whether CAS should accept local URLs. For example http(s)://localhost/logout.

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.async-timeout=PT5S
  • Indicates timeout for async operations.

    This settings supports the java.time.Duration syntax [?].

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.authority-validation-reg-ex-case-sensitive=true
  • Whether the regular expression specified with #authorityValidationRegex should be handled as case-sensitive (true) or case-insensitive (false). If no #authorityValidationRegex is set, this value does not have any effect.

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.authority-validation-regex=
  • If specified the regular expression will be used to validate the url's authority.

    This settings supports regular expression patterns. [?].

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.connection-timeout=PT5S
  • Connection timeout for all operations that reach out to URL endpoints.

    This settings supports the java.time.Duration syntax [?].

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.default-headers=
  • The default headers to use for any HTTP connection. This is defined as map, where the key is the header name and the value is the header value that should be sent along with request.

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.host-name-verifier=default
  • Enable hostname verification when attempting to contact URL endpoints. May also be set to none to disable verification.

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.proxy-host=
  • Send requests via a proxy; define the hostname.

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.proxy-port=0
  • Send requests via a proxy; define the proxy port. Negative/zero values should deactivate the proxy configuration for the http client.

    org.apereo.cas.configuration.model.core.authentication.HttpClientProperties.

  • cas.http-client.truststore.file=
  • The CAS local truststore resource to contain certificates to the CAS deployment. In the event that local certificates are to be imported into the CAS running environment, a local truststore is provided by CAS to improve portability of configuration across environments.

    org.apereo.cas.configuration.model.core.authentication.HttpClientTrustStoreProperties.

  • cas.http-client.truststore.psw=changeit
  • The truststore password.

    org.apereo.cas.configuration.model.core.authentication.HttpClientTrustStoreProperties.

  • cas.http-client.truststore.type=
  • Truststore type used to create a SSL context for http client.

    org.apereo.cas.configuration.model.core.authentication.HttpClientTrustStoreProperties.