Kerberos Grant

Kerberos is a security protocol that has support built into various operating systems and open-source distributions (e.g.,  Ubuntu, Windows, RedHat, Open Solaris, etc). Additionally, a majority of browsers support some Kerberos functions as well. As WSO2 Identity Server (WSO2 IS) uses the OAuth 2.0 protocol, the Kerberos-OAuth2 grant type allows organizations to exchange a Kerberos ticket for an OAuth 2.0 token. This allows organizations to re-use their existing Kerberos infrastructure and adopt OAuth 2.0. 

The following section describes the flow involved in exchanging a Kerberos ticket for an OAuth2 token.

1. The Kerberos client requests the Kerberos Service Ticket from the Kerberos Key Distribution Center (KDC) to invoke the service.
   The Kerberos Key Distribution Center can be any Kerberos Server.

2. The Kerberos Key Distribution Center sends a response with the Kerberos Service Ticket.
   If the client and the requested service is valid, the Key Distribution Center (KDC) sends a Kerberos ticket encrypted with the service owners private key. The API handles the exchanging of the Ticket Granting Ticket (TGT), Service Granting Ticket (SGT), and all other low level Kerberos details.

3. The Kerberos client requests the OAuth2 token.
   

   The message format of the OAuth2 token request should be as follows:
   
   
   

4. The Kerberos client receives the OAuth2 token.
   The Kerberos Grant validates the received token with the provided Identity Provider (IDP) credentials and if it is a valid token, it issues an OAuth2 token to the client.

   Example

   { "access_token":"636ce45f-c7f6-3a95-907f-d1f8aca28403", "refresh_token":"831271d9-16ba-3bad-af18-b9f6592a8677", "scope":"my_scope", "token_type":"Bearer", "expires_in":521 }

Follow the instructions below to configure Kerberos Grant with WSO2 IS:

1. Download the Keberos-grant JAR (kerberos-grant-1.0.0.jar).

2. Copy the JAR into the <IS_HOME>/repository/components/lib directory.

3. Add following entry under <SupportedGrantTypes> in the <IS_HOME>/repository/conf/identity/identity.xml file.

   <SupportedGrantType> <GrantTypeName>kerberos</GrantTypeName> <GrantTypeHandlerImplClass>org.wso2.carbon.identity.oauth2.grant.kerberos.KerberosGrant</GrantTypeHandlerImplClass> <GrantTypeValidatorImplClass>org.wso2.carbon.identity.oauth2.grant.kerberos.KerberosGrantValidator</GrantTypeValidatorImplClass> </SupportedGrantType>

4. Configure OAuth2 with IWA as an allowed grant type.

   1. Sign in to the WSO2 IS Management Console.
      https://<Server-Host>:9443/carbon

   2. Navigate to the Main menu, click Add under the Service Providers menu.
      
      

   3. Add a new Service Provider and configure OAuth2 for your client application with kerberos as an allowed grant type. 

5. Configure the Service Principal Name (SPNName) and Service Principal Password (SPNPassword).

   1. Navigate to the Main menu, click Add under the Identity Providers menu.

   2. Add a new Identity Provider (IDP). Enter the basic information as follows. 

      • Identity Provider Name: example.com

      • Alias: https://192.168.53.12:9443/oauth/token

      Open

      

   3. Expand the Federated Authenticators tab, and then the IWA Kerberos Configuration tab. Enter the required details as follows.
      
      

      • Server Principal Name: HTTP/idp.example.com@EXAMPLE.COM

      • Server Principal Password: <password> 

      Open

      

6. Invoke the token endpoint using the message format discussed in step 3.