Throttling Authentication Attempts

Capacity Throttling

CAS is able to support request rate-limiting based on the token-bucket algorithm, via the Bucket4j project. This means that authentication requests that reach a certain configurable capacity within a time window may either be blocked or throttled to slow down. This is done to protect the system from overloading, allowing you to introduce a scenario to allow CAS 120 authentication requests per minute with a refill rate of 10 requests per second that would continually increase in the capacity bucket.

Enable the following module in your configuration overlay:

implementation "org.apereo.cas:cas-server-support-throttle-bucket4j:${project.'cas.version'}"
dependencyManagement {
  imports {
    mavenBom "org.apereo.cas:cas-server-support-bom:${project.'cas.version'}"

dependencies {  
  implementation "org.apereo.cas:cas-server-support-throttle-bucket4j"

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.

  • cas.authn.throttle.bucket4j.bandwidth[0].capacity=120
  • Number of tokens/requests that can be used within the time window.

  • cas.authn.throttle.bucket4j.bandwidth[0].duration=PT60S
  • Time window in which capacity can be allowed.

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

  • cas.authn.throttle.bucket4j.bandwidth[0].initial-tokens=
  • By default initial size of bucket equals to capacity. But sometimes, you may want to have lesser initial size, for example for case of cold start in order to prevent denial of service.

  • cas.authn.throttle.bucket4j.bandwidth[0].refill-count=10
  • The number of tokens that should be used to refill the bucket given the specified refill duration.

  • cas.authn.throttle.bucket4j.bandwidth[0].refill-duration=PT30S
  • Duration to use to refill the bucket.

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

  • cas.authn.throttle.bucket4j.bandwidth[0].refill-strategy=GREEDY
  • Describes how the bucket should be refilled. Specifies the speed of tokens regeneration. Available values are as follows:

    • GREEDY: This type of refill regenerates tokens in a greedy manner; it tries to add the tokens to bucket as soon as possible. For example refill "10 tokens per 1 second" adds 1 token per each 100 millisecond; in other words refill will not wait 1 second to regenerate 10 tokens.
    • INTERVALLY: This type of refill regenerates tokens in intervally manner. "Intervally" in opposite to "greedy" will wait until whole period would be elapsed before regenerating tokens.

  • cas.authn.throttle.bucket4j.bandwidth=
  • Describe the available bandwidth and the overall limitations. Multiple bandwidths allow for different policies per unit of measure. (i.e. allows 1000 tokens per 1 minute, but not often then 50 tokens per 1 second).

  • cas.authn.throttle.bucket4j.blocking=true
  • Whether the request should block until capacity becomes available. Consume a token from the token bucket. If a token is not available this will block until the refill adds one to the bucket.

  • cas.authn.throttle.bucket4j.enabled=true
  • Decide whether bucket4j functionality should be enabled.