Token Exchange Grant Type: Exchanging a Kerberos Token for a UPST

1. Use Java code to connect to the KDC Server and generate the SPNEGO token.
2. Copy that SPNEGO token to form the token request.

package com.oracle;

import com.sun.security.auth.module.Krb5LoginModule;
import org.ietf.jgss.GSSContext;
import org.ietf.jgss.GSSException;
import org.ietf.jgss.GSSManager;
import org.ietf.jgss.GSSName;
import org.ietf.jgss.Oid;

import javax.security.auth.Subject;
import java.io.IOException;
import java.security.Principal;
import java.security.PrivilegedAction;
import java.util.Base64;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class GenerateSpnegoToken {
    static String servicePrincipal = "HTTP/iamtesp@WINDOWSKDCSERVER.COM";
    static String userPrincipal = "HTTP/<sample-job>@WINDOWSKDCSERVER.COM";
    static String userPrincipalKeyTab = "keytabs/ms/<sample-job>.keytab";
    public static void main(String[] args) throws IOException {
        System.setProperty("sun.security.krb5.debug", "true");
        System.setProperty("sun.security.spnego.debug", "true");
        System.setProperty("java.security.krb5.conf", "ms_krb5.conf");

        String spnegoToken = generateSpnegoToken();
    }
    private static String generateSpnegoToken() {
        Subject subject = getAuthenticateSubject();
        return Subject.doAs(
                subject,
                (PrivilegedAction<String>)
                        () -> {
                            String SPNEGO_OID = "1.3.6.1.5.5.2";
                            String KRB5_MECHANISM_OID = "1.2.840.113554.1.2.2";
                            String KRB5_PRINCIPAL_NAME_OID = "1.2.840.113554.1.2.2.1";

                            try {
                                // Create GSS context for the service principal and the logged-in user
                                Oid krb5Mechanism = new Oid(KRB5_MECHANISM_OID);
                                Oid krb5PrincipalNameType = new Oid(KRB5_PRINCIPAL_NAME_OID);
                                Oid spnegoOid = new Oid(SPNEGO_OID);
                                GSSManager manager = GSSManager.getInstance();
                                GSSName gssServerName =
                                        manager.createName(servicePrincipal, krb5PrincipalNameType, krb5Mechanism);
                                GSSContext gssContext =
                                        manager.createContext(
                                                gssServerName, spnegoOid, null, 240000);
                                gssContext.requestMutualAuth(true);
                                gssContext.requestCredDeleg(true);
                                gssContext.requestLifetime(10);

                                // Generate the SPNEGO token
                                byte[] token = new byte[0];
                                token = gssContext.initSecContext(token, 0, token.length);
                                return Base64.getEncoder().encodeToString(token);
                            } catch (GSSException e) {
                                throw new RuntimeException(e);
                            }
                        });
    }

    private static Subject getAuthenticateSubject() {
        final Map<String, String> options = new HashMap<>();
        options.put("keyTab", userPrincipalKeyTab);
        options.put("principal", userPrincipal);
        options.put("doNotPrompt", "true");
        options.put("isInitiator", "true");
        options.put("refreshKrb5Config", "true");
        options.put("storeKey", "true");
        options.put("useKeyTab", "true");

        // Execute the login
        Subject subject = new Subject();
        Krb5LoginModule krb5LoginModule = new Krb5LoginModule();
        krb5LoginModule.initialize(subject, null, new HashMap<String, String>(), options);
        try {
            krb5LoginModule.login();
            krb5LoginModule.commit();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        Set<Principal> principals = (Set<Principal>) subject.getPrincipals();
        Iterator<Principal> iterator = principals.iterator();
        while (iterator.hasNext()) {
            System.out.println("\nprincipal : " + ((Principal) iterator.next()));
        }

        return subject;

    }
}

## POST on https://<domainURL>/admin/v1/IdentityPropagationTrusts
## Payload:
{
 "active": true,
 "allowImpersonation": false,
 "issuer": "idcs_psr_itp",
 "name": "<identity_propagation_trust_name>",
 "oauthClients": [
 "<oauthclient-id>"
 ],
 "keytab": {
 "secretOcid": "<secret_ocid>"
 },
 "subjectMappingAttribute": "userName",
 "subjectType": "User",
 "type": "SPNEGO",
 "schemas": [
 "urn:ietf:params:scim:schemas:oracle:idcs:IdentityPropagationTrust"
 ]
}

  "response": {
    "name": "<identity_propagation_trust_name>",
    "type": "<token_type>",
    "issuer": "idcs_psr_itp",
    "accountId": "<example_account_id>",
    "subjectClaimName": "cognito:username",
    "subjectMappingAttribute": "username",
    "subjectType": "User",
    "clientClaimName": "appId",
    "clientClaimValues": ["<client_claim_value>"],
    "active": true,
    "publicKeyEndpoint": "https://example.identityprovider.com/publickey/<publickey_value>",
    "publicCertificate": "<public_certificate_value>",
    "oauthClients": ["<oauthclient-id>"],

    "allowImpersonation": true,
    "impersonationServiceUsers": [
      {
        "rule": "groups co \"network-admin\"",
        "userId": "<user_id>"
      },
      {
        "rule": "groups co \"tenancy-admin\"",
        "userId": "<user_id>"
      }
    ],
    "keytab": {
      "secretOcid": "<secret_ocid>",
      "secretVersion": "<secret_version>"
    },
    "clockSkewSeconds": 60,
    "id": "<identity_propagation_trust_id>",
    "meta": {
      "created": "2023-11-09T23:26:53.224Z",
      "lastModified": "2023-11-09T23:26:53.224Z",
      "resourceType": "IdentityPropagationTrust",
      "location": "http://example.hostname.com:8990/admin/v1/IdentityPropagationTrusts/<identity_propagation_trust_id>"
    },
    "schemas": [
      "urn:ietf:params:scim:schemas:oracle:idcs:IdentityPropagationTrust"
    ],
    "idcsCreatedBy": {
      "value": "<app_id>",
      "display": "admin",
      "type":"App",
      "$ref": "http://example.hostname.com:8990/admin/v1/Apps/<app_id>"
    },
    "idcsLastModifiedBy": {
      "value": "<app_id>",
      "display": "admin",
      "type":"App",
      "$ref": "http://example.hostname.com:8990/admin/v1/Apps/<app_id>"
    }
  }