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. Please note that the bucket allocation strategy is specific to the client IP address.
Enable the following module in your configuration overlay:
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<dependency>
<groupId>org.apereo.cas</groupId>
<artifactId>cas-server-support-throttle-bucket4j</artifactId>
<version>${cas.version}</version>
</dependency>
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implementation "org.apereo.cas:cas-server-support-throttle-bucket4j:${project.'cas.version'}"
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dependencyManagement {
imports {
mavenBom "org.apereo.cas:cas-server-support-bom:${project.'cas.version'}"
}
}
dependencies {
implementation "org.apereo.cas:cas-server-support-throttle-bucket4j"
}
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dependencies {
/*
The following platform references should be included automatically and are listed here for reference only.
implementation enforcedPlatform("org.apereo.cas:cas-server-support-bom:${project.'cas.version'}")
implementation platform(org.springframework.boot.gradle.plugin.SpringBootPlugin.BOM_COORDINATES)
*/
implementation "org.apereo.cas:cas-server-support-throttle-bucket4j"
}
The following settings and properties are available from the CAS configuration catalog:
cas.authn.throttle.bucket4j.bandwidth[0].capacity=120
Number of tokens/requests that can be used within the time window.
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cas.authn.throttle.bucket4j.bandwidth[0].duration=PT60S
Time window in which capacity can be allowed. This settings supports the
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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.
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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.
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cas.authn.throttle.bucket4j.bandwidth[0].refill-duration=PT30S
Duration to use to refill the bucket. This settings supports the
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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:
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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).
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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.
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cas.authn.throttle.bucket4j.enabled=true
Decide whether bucket4j functionality should be enabled.
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Configuration Metadata
The collection of configuration properties listed in this section are automatically generated from the CAS source and components that contain the actual field definitions, types, descriptions, modules, etc. This metadata may not always be 100% accurate, or could be lacking details and sufficient explanations.
Be Selective
This section is meant as a guide only. Do NOT copy/paste the entire collection of settings into your CAS configuration; rather pick only the properties that you need. Do NOT enable settings unless you are certain of their purpose and do NOT copy settings into your configuration only to keep them as reference. All these ideas lead to upgrade headaches, maintenance nightmares and premature aging.
YAGNI
Note that for nearly ALL use cases, declaring and configuring properties listed here is sufficient. You should NOT have to explicitly massage a CAS XML/Java/etc configuration file to design an authentication handler, create attribute release policies, etc. CAS at runtime will auto-configure all required changes for you. If you are unsure about the meaning of a given CAS setting, do NOT turn it on without hesitation. Review the codebase or better yet, ask questions to clarify the intended behavior.
Naming Convention
Property names can be specified in very relaxed terms. For instance cas.someProperty, cas.some-property, cas.some_property are all valid names. While all
forms are accepted by CAS, there are certain components (in CAS and other frameworks used) whose activation at runtime is conditional on a property value, where
this property is required to have been specified in CAS configuration using kebab case. This is both true for properties that are owned by CAS as well as those
that might be presented to the system via an external library or framework such as Spring Boot, etc.
When possible, properties should be stored in lower-case kebab format, such as cas.property-name=value.
The only possible exception to this rule is when naming actuator endpoints; The name of the
actuator endpoints (i.e. ssoSessions) MUST remain in camelCase mode.
Settings and properties that are controlled by the CAS platform directly always begin with the prefix cas. All other settings are controlled and provided
to CAS via other underlying frameworks and may have their own schemas and syntax. BE CAREFUL with
the distinction. Unrecognized properties are rejected by CAS and/or frameworks upon which CAS depends. This means if you somehow misspell a property definition
or fail to adhere to the dot-notation syntax and such, your setting is entirely refused by CAS and likely the feature it controls will never be activated in the
way you intend.
Validation
Configuration properties are automatically validated on CAS startup to report issues with configuration binding, specially if defined CAS settings cannot be
recognized or validated by the configuration schema. The validation process is on by default and can be skipped on startup using a special system
property SKIP_CONFIG_VALIDATION that should be set to true. Additional validation processes are also handled
via Configuration Metadata and property migrations applied automatically on
startup by Spring Boot and family.
Indexed Settings
CAS settings able to accept multiple values are typically documented with an index, such as cas.some.setting[0]=value. The index [0] is meant to be
incremented by the adopter to allow for distinct multiple configuration blocks.
Failure Throttling
CAS provides a facility for limiting failed login attempts to support password guessing and related abuse scenarios. A couple strategies are provided for tracking failed attempts:
- Source IP - Limit successive failed logins against any username from the same IP address.
- Source IP and username - Limit successive failed logins against a particular user from the same IP address.
All login throttling components that ship with CAS limit successive failed login attempts that exceed a threshold rate, which is a time in seconds between two failures. The following properties are provided to define the failure rate.
threshold- Number of failed login attempts.rangeSeconds- Period of time in seconds.
A failure rate of more than 1 per 3 seconds is indicative of an automated authentication attempt, which is a reasonable basis for throttling policy. Regardless of policy care should be taken to weigh security against access; overly restrictive policies may prevent legitimate authentication attempts.
The failure threshold rate is calculated as: threshold / rangeSeconds. For instance,
the failure rate for the above scenario would be 0.333333. An authentication attempt may be considered throttled
if the request submission rate (calculated as the difference between the current date and the last submission date) exceeds
the failure threshold rate.
Enable the following module in your configuration overlay:
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<dependency>
<groupId>org.apereo.cas</groupId>
<artifactId>cas-server-support-throttle</artifactId>
<version>${cas.version}</version>
</dependency>
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implementation "org.apereo.cas:cas-server-support-throttle:${project.'cas.version'}"
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dependencyManagement {
imports {
mavenBom "org.apereo.cas:cas-server-support-bom:${project.'cas.version'}"
}
}
dependencies {
implementation "org.apereo.cas:cas-server-support-throttle"
}
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dependencies {
/*
The following platform references should be included automatically and are listed here for reference only.
implementation enforcedPlatform("org.apereo.cas:cas-server-support-bom:${project.'cas.version'}")
implementation platform(org.springframework.boot.gradle.plugin.SpringBootPlugin.BOM_COORDINATES)
*/
implementation "org.apereo.cas:cas-server-support-throttle"
}
Configuration
The following settings and properties are available from the CAS configuration catalog:
cas.authn.throttle.core.app-code=CAS
Application code used to identify this application in the audit logs.
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cas.authn.throttle.core.username-parameter=
Username parameter to use in order to extract the username from the request.
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cas.authn.throttle.schedule.enabled=true
Whether scheduler should be enabled to schedule the job to run.
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cas.authn.throttle.schedule.enabled-on-host=.*
Overrides
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cas.authn.throttle.schedule.repeat-interval=PT2M
String representation of a repeat interval of re-loading data for an data store implementation. This is the timeout between consecutive job’s executions. This settings supports the
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cas.authn.throttle.schedule.start-delay=PT15S
String representation of a start delay of loading data for a data store implementation. This is the delay between scheduler startup and first job’s execution This settings supports the
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cas.authn.throttle.failure.code=AUTHENTICATION_FAILED
Failure code to record in the audit log. Generally this indicates an authentication failure event.
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cas.authn.throttle.failure.range-seconds=-1
Period of time in seconds for the threshold rate.
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cas.authn.throttle.failure.threshold=-1
Number of failed login attempts for the threshold rate.
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cas.authn.throttle.failure.throttle-window-seconds=0
Indicate the number of seconds the account should remain in a locked/throttled state before it can be released to continue again. If no value is specified, the failure threshold and rate that is calculated would hold. This settings supports the
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Configuration Metadata
The collection of configuration properties listed in this section are automatically generated from the CAS source and components that contain the actual field definitions, types, descriptions, modules, etc. This metadata may not always be 100% accurate, or could be lacking details and sufficient explanations.
Be Selective
This section is meant as a guide only. Do NOT copy/paste the entire collection of settings into your CAS configuration; rather pick only the properties that you need. Do NOT enable settings unless you are certain of their purpose and do NOT copy settings into your configuration only to keep them as reference. All these ideas lead to upgrade headaches, maintenance nightmares and premature aging.
YAGNI
Note that for nearly ALL use cases, declaring and configuring properties listed here is sufficient. You should NOT have to explicitly massage a CAS XML/Java/etc configuration file to design an authentication handler, create attribute release policies, etc. CAS at runtime will auto-configure all required changes for you. If you are unsure about the meaning of a given CAS setting, do NOT turn it on without hesitation. Review the codebase or better yet, ask questions to clarify the intended behavior.
Naming Convention
Property names can be specified in very relaxed terms. For instance cas.someProperty, cas.some-property, cas.some_property are all valid names. While all
forms are accepted by CAS, there are certain components (in CAS and other frameworks used) whose activation at runtime is conditional on a property value, where
this property is required to have been specified in CAS configuration using kebab case. This is both true for properties that are owned by CAS as well as those
that might be presented to the system via an external library or framework such as Spring Boot, etc.
When possible, properties should be stored in lower-case kebab format, such as cas.property-name=value.
The only possible exception to this rule is when naming actuator endpoints; The name of the
actuator endpoints (i.e. ssoSessions) MUST remain in camelCase mode.
Settings and properties that are controlled by the CAS platform directly always begin with the prefix cas. All other settings are controlled and provided
to CAS via other underlying frameworks and may have their own schemas and syntax. BE CAREFUL with
the distinction. Unrecognized properties are rejected by CAS and/or frameworks upon which CAS depends. This means if you somehow misspell a property definition
or fail to adhere to the dot-notation syntax and such, your setting is entirely refused by CAS and likely the feature it controls will never be activated in the
way you intend.
Validation
Configuration properties are automatically validated on CAS startup to report issues with configuration binding, specially if defined CAS settings cannot be
recognized or validated by the configuration schema. The validation process is on by default and can be skipped on startup using a special system
property SKIP_CONFIG_VALIDATION that should be set to true. Additional validation processes are also handled
via Configuration Metadata and property migrations applied automatically on
startup by Spring Boot and family.
Indexed Settings
CAS settings able to accept multiple values are typically documented with an index, such as cas.some.setting[0]=value. The index [0] is meant to be
incremented by the adopter to allow for distinct multiple configuration blocks.
Actuator Endpoints
The following endpoints are provided by CAS:
Throttling Strategies
The following throttling strategies are offered by CAS.
| Storage | Description |
|---|---|
| IP Address | Uses a memory map to prevent successive failed login attempts from the same IP address. |
| IP Address and Username | Uses a memory map to prevent successive failed login attempts for a username from the same IP address. |
| JDBC | See this guide. |
| MongoDb | See this guide. |
| Redis | See this guide. |
| Hazelcast | See this guide. |
| CouchDb | See this guide. |
High Availability
All of the throttling components are suitable for a CAS deployment that satisfies the recommended HA architecture. 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 not sufficient for detecting or preventing a distributed password brute force attack.