OAuth Authentication

Allow CAS to act as an OAuth authentication provider. Please review the specification to learn more.

CAS as OAuth Server

This page specifically describes how to enable OAuth/OpenID server support for CAS. If you would like to have CAS act as an OAuth/OpenID client communicating with other providers (such as Google, Facebook, etc), see this page.

Actuator Endpoints

The following endpoints are provided by CAS:


Configuration

Support is enabled by including the following dependency in the WAR overlay:

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<dependency>
  <groupId>org.apereo.cas</groupId>
  <artifactId>cas-server-support-oauth-webflow</artifactId>
  <version>${cas.version}</version>
</dependency>

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implementation "org.apereo.cas:cas-server-support-oauth-webflow:${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-oauth-webflow"
}

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. You should only include this field in your configuration if you need to modify the default value.

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.

Endpoints

After enabling OAuth support, the following endpoints will be available:

Endpoint Description Method
/oauth2.0/authorize Authorize the user and start the CAS authentication flow. GET
/oauth2.0/accessToken,/oauth2.0/token Get an access token in plain-text or JSON POST
/oauth2.0/profile Get the authenticated user profile in JSON via access_token parameter. GET
/oauth2.0/introspect Query CAS to detect the status of a given access token via introspection. This endpoint expects HTTP basic authentication with OAuth2 service client_id and client_secret associated as username and password. POST
/oauth2.0/device Approve device user codes via the device flow protocol. POST
/oauth2.0/revoke Revoke access or refresh tokens. This endpoint expects HTTP basic authentication with OAuth2 service client_id and client_secret associated as username and password.  

Response/Grant Types

The following types are supported; they allow you to get an access token representing the current user and OAuth client application. With the access token, you’ll be able to query the /profile endpoint and get the user profile.

Authorization Code

The authorization code type is made for UI interactions: the user will enter credentials, shall receive a code and will exchange that code for an access token.

Endpoint Parameters Response
/oauth2.0/authorize response_type=code&client_id=<ID>&redirect_uri=<CALLBACK> OAuth code as a parameter of the CALLBACK url.
/oauth2.0/accessToken grant_type=authorization_code&client_id=ID
&client_secret=SECRET&code=CODE&redirect_uri=CALLBACK		 The access token.

Proof Key Code Exchange (PKCE)

The Proof Key for Code Exchange (PKCE, pronounced pixie) extension describes a technique for public clients to mitigate the threat of having the authorization code intercepted. The technique involves the client first creating a secret, and then using that secret again when exchanging the authorization code for an access token. This way if the code is intercepted, it will not be useful since the token request relies on the initial secret.

The authorization code type at the authorization endpoint /oauth2.0/authorize is able to accept the following parameters to activate PKCE:

Parameter Description
code_challenge The code challenge generated using the method below.
code_challenge_method plain, S256. This parameter is optional, where plain is assumed by default.

The /oauth2.0/accessToken endpoint is able to accept the following parameters to activate PKCE:

Parameter Description
code_verifier The original code verifier for the PKCE request, that the app originally generated before the authorization request.

If the method is plain, then the CAS needs only to check that the provided code_verifier matches the expected code_challenge string. If the method is S256, then the CAS should take the provided code_verifier and transform it using the same method the client will have used initially. This means calculating the SHA256 hash of the verifier and base64-url-encoding it, then comparing it to the stored code_challenge.

If the verifier matches the expected value, then the CAS can continue on as normal, issuing an access token and responding appropriately.

Token/Implicit

The token type is also made for UI interactions as well as indirect non-interactive (i.e. Javascript) applications.

Endpoint Parameters Response
/oauth2.0/authorize response_type=token&client_id=ID&redirect_uri=CALLBACK The access token as an anchor parameter of the CALLBACK url.

Resource Owner Credentials

The password grant type allows the OAuth client to directly send the user’s credentials to the OAuth server. This grant is a great user experience for trusted first party clients both on the web and in native device applications.

Endpoint Parameters Response
/oauth2.0/accessToken grant_type=password&client_id=ID
&client_secret=<SECRET>
&username=USERNAME&password=PASSWORD		 The access token.

Because there is no redirect_uri specified by this grant type, the service identifier recognized by CAS and matched in the service registry is taken as the client_id instead. You may optionally also pass along a service or X-service header value that identifies the target application url. The header value must match the OAuth service definition in the registry that is linked to the client id.

Client Credentials

The simplest of all of the OAuth grants, this grant is suitable for machine-to-machine authentication where a specific user’s permission to access data is not required.

Endpoint Parameters Response
/oauth2.0/accessToken grant_type=client_credentials&client_id=client&client_secret=secret The access token.

Because there is no redirect_uri specified by this grant type, the service identifier recognized by CAS and matched in the service registry is taken as the client_id instead. You may optionally also pass along a service or X-service header value that identifies the target application url. The header value must match the OAuth service definition in the registry that is linked to the client id.

Refresh Token

The refresh token grant type retrieves a new access token from a refresh token (emitted for a previous access token), when this previous access token is expired.

Endpoint Parameters Response
/oauth2.0/accessToken grant_type=refresh_token&client_id=<ID>
&client_secret=SECRET&refresh_token=REFRESH_TOKEN		 The new access token.

Device Flow

Endpoint Parameters Response
/oauth2.0/accessToken response_type=device_code&client_id=<ID> Device authorization url, device code and user code.
/oauth2.0/accessToken response_type=device_code&client_id=<ID>&code=<DEVICE_CODE> New access token once the user code is approved.

Grant Type Selection

A grant is a method of acquiring an access token. Deciding which grants to implement depends on the type of client the end user will be using, and the experience you want for your users.

To learn more about profiles and grant types, please review this guide.

Client Registration

Please see this guide.

OAuth Token Expiration Policy

Please see this guide.

JWT Access Tokens

By default, OAuth access tokens are created as opaque identifiers. There is also the option to generate JWTs as access tokens on a per-service basis:

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{
    "@class" : "org.apereo.cas.support.oauth.services.OAuthRegisteredService",
    "clientId": "clientid",
    "clientSecret": "clientSecret",
    "serviceId" : "^(https|imaps)://<redirect-uri>.*",
    "name" : "OAuthService",
    "id" : 100,
    "jwtAccessToken": true,
    "properties" : {
      "@class" : "java.util.HashMap",
      "accessTokenAsJwtSigningKey" : {
         "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
         "values" : [ "java.util.HashSet", [ "..." ] ]
      },
      "accessTokenAsJwtEncryptionKey" : {
           "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
           "values" : [ "java.util.HashSet", [ "..." ] ]
      },
      "accessTokenAsJwtSigningEnabled" : {
         "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
         "values" : [ "java.util.HashSet", [ "true" ] ]
      },
      "accessTokenAsJwtEncryptionEnabled" : {
         "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
         "values" : [ "java.util.HashSet", [ "true" ] ]
      },
      "accessTokenAsJwtCipherStrategyType" : {
         "@class" : "org.apereo.cas.services.DefaultRegisteredServiceProperty",
         "values" : [ "java.util.HashSet", [ "ENCRYPT_AND_SIGN" ] ]
      }
    }
}

Signing and encryption keys may also be defined on a per-service basis, or globally via CAS settings.

The following properties are available and recognized by CAS for various modules and features:

Name Default Value Type Group

OAuth User Profile Structure

Please see this guide.

Throttling

Authentication throttling may be enabled for the /oauth2.0/accessToken provided support is included in the overlay to turn on authentication throttling support. The throttling mechanism that handles the usual CAS server endpoints for authentication and ticket validation, etc is then activated for the OAuth endpoints that are supported for throttling.

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. You should only include this field in your configuration if you need to modify the default value.

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.

Server Configuration

Remember that OAuth features of CAS require session affinity (and optionally session replication), as the authorization responses throughout the login flow are stored via server-backed session storage mechanisms. You will need to configure your deployment environment and load balancers accordingly.

Session Replication

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. You should only include this field in your configuration if you need to modify the default value.

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.

Sample Client Applications