Blacklist authentication components are those that specifically deny access to a set of credentials. Those that fail to match against the predefined set will blindly be accepted.
These are:
*`RejectUsersAuthenticationHandler`
## Authentication Components
Support is enabled by including the following dependency in the Maven WAR overlay:
The CAS authentication process is performed by several related components:
######`PrincipalNameTransformer`
Transforms the user id string that is typed into the login form into a tentative Principal Name to be
validated by a specific type of Authentication Handler.
######`AuthenticationManager`
Entry point into authentication subsystem. It accepts one or more credentials and delegates authentication to
configured `AuthenticationHandler` components. It collects the results of each attempt and determines effective
security policy.
######`AuthenticationHandler`
Authenticates a single credential and reports one of three possible results: success, failure, not attempted.
######`PrincipalResolver`
Converts information in the authentication credential into a security principal that commonly contains additional
metadata attributes (i.e. user details such as affiliations, group membership, email, display name).
######`AuthenticationMetaDataPopulator`
Strategy component for setting arbitrary metadata about a successful authentication event; these are commonly used
to set protocol-specific data.
Unless otherwise noted, the configuration for all authentication components is handled in `deployerConfigContext.xml`.
## Authentication Manager
CAS ships with a single yet flexible authentication manager, `PolicyBasedAuthenticationManager`, that should be
sufficient for most needs. It performs authentication according to the following contract.
For each given credential do the following:
1. Iterate over all configured authentication handlers.
2. Attempt to authenticate a credential if a handler supports it.
3. On success attempt to resolve a principal.
1. Check whether a resolver is configured for the handler that authenticated the credential.
2. If a suitable resolver is found, attempt to resolve the principal.
3. If a suitable resolver is not found, use the principal resolved by the authentication handler.
4. Check whether the security policy (e.g. any, all) is satisfied.
1. If security policy is met return immediately.
2. Continue if security policy is not met.
5. After all credentials have been attempted check security policy again and throw `AuthenticationException`
if not satisfied.
There is an implicit security policy that requires at least one handler to successfully authenticate a credential,
but the behavior can be further controlled by setting `#setAuthenticationPolicy(AuthenticationPolicy)`
with one of the following policies.
######`AnyAuthenticationPolicy`
Satisfied if any handler succeeds. Supports a `tryAll` flag to avoid short circuiting at step 4.1 above and try every
handler even if one prior succeeded. This policy is the default and provides backward-compatible behavior with the
`AuthenticationManagerImpl` component of CAS 3.x.
######`AllAuthenticationPolicy`
Satisfied if and only if all given credentials are successfully authenticated. Support for multiple credentials is
new in CAS and this handler would only be acceptable in a multi-factor authentication situation.
######`RequiredHandlerAuthenticationPolicy`
Satisfied if an only if a specified handler successfully authenticates its credential. Supports a `tryAll` flag to
avoid short circuiting at step 4.1 above and try every handler even if one prior succeeded. This policy could be
used to support a multi-factor authentication situation, for example, where username/password authentication is
required but an additional OTP is optional.
The following configuration snippet demonstrates how to configure `PolicyBasedAuthenticationManager` for a
straightforward multi-factor authentication case where username/password authentication is required and an additional OTP credential is optional; in both cases principals are resolved from LDAP.
There are some additional handlers for small deployments and special cases:
*[Whilelist](Whitelist-Authentication.html)
*[Blacklist](Blacklist-Authentication.html)
##Argument Extractors
Extractors are responsible to examine the http request received for parameters that describe the authentication request such as the requesting `service`, etc. Extractors exist for a number of supported authentication protocols and each create appropriate instances of `WebApplicationService` that contains the results of the extraction.
Argument extractor configuration is defined at `src/main/webapp/WEB-INF/spring-configuration/argumentExtractorsConfiguration.xml`. Here's a brief sample:
## High Availability Considerations for Throttling
All of the throttling components are suitable for a CAS deployment that satisfies the
[recommended HA architecture](../planning/High-Availability-Guide.html). In particular deployments with multiple CAS
nodes behind a load balancer configured with session affinity can use either in-memory or _inspektr_ components. It is
instructive to discuss the rationale. Since load balancer session affinity is determined by source IP address, which
is the same criterion by which throttle policy is applied, an attacker from a fixed location should be bound to the
same CAS server node for successive authentication attempts. A distributed attack, on the other hand, where successive
request would be routed indeterminately, would cause haphazard tracking for in-memory CAS components since attempts
would be split across N systems. However, since the source varies, accurate accounting would be pointless since the
throttling components themselves assume a constant source IP for tracking purposes. The login throttling components
are simply not sufficient for detecting or preventing a distributed password brute force attack.
For stateless CAS clusters where there is no session affinity, the in-memory components may afford some protection but
they cannot apply the rate strictly since requests to CAS hosts would be split across N systems.
The _inspektr_ components, on the other hand, fully support stateless clusters.
### Configuring Login Throttling
Login throttling configuration consists of two core components:
1. A login throttle modeled as a Spring `HandlerInterceptorAdapter` component.
2. A scheduled task that periodically cleans up state to allow the throttle to relax.
The period of scheduled task execution MUST be less than that defined by `failureRangeInSeconds` for proper throttle policy enforcement. For example, if `failureRangeInSeconds` is 3, then the quartz trigger that drives the task would be configured for less than 3000 (ms).
It is convenient to place Spring configuration for login throttling components in `deployerConfigContext.xml`.
This feature, also known as *Remember Me*, extends the length of the SSO session beyond the typical period of hours
such that users can go days or weeks without having to log in to CAS. See the
[security guide](../planning/Security-Guide.html)
for discussion of security concerns related to long term authentication.
### Policy and Deployment Considerations
While users can elect to establish a long term authentication session, the duration is established through
configuration as a matter of security policy. Deployers must determine the length of long term authentication sessions
by weighing convenience against security risks. The length of the long term authentication session is configured
(somewhat unhelpfully) in seconds, but the Google calculator provides a convenient converter:
[2 weeks in seconds](https://www.google.com/search?q=2+weeks+in+seconds&oq=2+weeks+in+seconds)
The use of long term authentication sessions dramatically increases the length of time ticket-granting tickets are
stored in the ticket registry. Loss of a ticket-granting ticket corresponding to a long-term SSO session would require
the user to reauthenticate to CAS. A security policy that requires that long term authentication sessions MUST NOT
be terminated prior to their natural expiration would mandate a ticket registry component that provides for durable storage. Memcached is a notable example of a store that has no facility for durable storage. In many cases loss of
ticket-granting tickets is acceptable, even for long term authentication sessions.
It's important to note that ticket-granting tickets and service tickets can be stored in separate registries, where
the former provides durable storage for persistent long-term authentication tickets and the latter provides less
durable storage for ephemeral service tickets. Thus deployers could mix `JpaTicketRegistry` and
`MemcachedTicketRegistry`, for example, to take advantage of their strengths, durability and speed respectively.
### Component Configuration
Long term authentication requires configuring CAS components in Spring configuration, modification of the CAS login
webflow, and UI customization of the login form. The length of the long term authentication session is represented
in following sections by the following property:
# Long term authentication session length in seconds
rememberMeDuration=1209600
The duration of the long term authentication session is configured in two different places:
1.`ticketExpirationPolicies.xml`
2.`ticketGrantingTicketCookieGenerator.xml`
Update the ticket-granting ticket expiration policy in `ticketExpirationPolicies.xml` to accommodate both long term
and stardard sessions.
{% highlight xml %}
<!--
| The following policy applies to standard CAS SSO sessions.
| Default 2h (7200s) sliding expiration with default 8h (28800s) maximum lifetime.
