Enforce batch_size ≥ 2 validation for batch_credential_issuance (#42003)

Closes #41590

Signed-off-by: forkimenjeckayang <forkimenjeckayang@gmail.com>

server-spi-private/src/main/java/org/keycloak/constants/Oid4VciConstants.java

@@ -29,6 +29,8 @@ public final class Oid4VciConstants {
 
     public static final String CREDENTIAL_SUBJECT = "credentialSubject";
 
+    public static final String BATCH_CREDENTIAL_ISSUANCE_BATCH_SIZE = "batch_credential_issuance.batch_size";
+
     private Oid4VciConstants() {
     }
 }

services/src/main/java/org/keycloak/protocol/oid4vc/issuance/OID4VCIssuerWellKnownProvider.java

@@ -91,14 +91,29 @@ public class OID4VCIssuerWellKnownProvider implements WellKnownProvider {
     }
 
     private CredentialIssuer.BatchCredentialIssuance getBatchCredentialIssuance(KeycloakSession session) {
-        RealmModel realm = session.getContext().getRealm();
-        String batchSize = realm.getAttribute("batch_credential_issuance.batch_size");
+        return getBatchCredentialIssuance(session.getContext().getRealm());
+    }
+
+    /**
+     * Returns the batch credential issuance configuration for the given realm.
+     * This method is public and static to facilitate testing without requiring session state management.
+     *
+     * @param realm The realm model
+     * @return The batch credential issuance configuration or null if not configured or invalid
+     */
+    public static CredentialIssuer.BatchCredentialIssuance getBatchCredentialIssuance(RealmModel realm) {
+        String batchSize = realm.getAttribute(Oid4VciConstants.BATCH_CREDENTIAL_ISSUANCE_BATCH_SIZE);
         if (batchSize != null) {
             try {
+                int parsedBatchSize = Integer.parseInt(batchSize);
+                if (parsedBatchSize < 2) {
+                    LOGGER.warnf("%s must be 2 or greater, but was %d. Skipping batch_credential_issuance.", Oid4VciConstants.BATCH_CREDENTIAL_ISSUANCE_BATCH_SIZE, parsedBatchSize);
+                    return null;
+                }
                 return new CredentialIssuer.BatchCredentialIssuance()
-                        .setBatchSize(Integer.parseInt(batchSize));
+                        .setBatchSize(parsedBatchSize);
             } catch (Exception e) {
-                LOGGER.warnf(e, "Failed to parse batch_credential_issuance.batch_size from realm attributes.");
+                LOGGER.warnf(e, "Failed to parse %s from realm attributes.", Oid4VciConstants.BATCH_CREDENTIAL_ISSUANCE_BATCH_SIZE);
             }
         }
         return null;

testsuite/integration-arquillian/tests/base/src/test/java/org/keycloak/testsuite/oid4vc/issuance/signing/OID4VCIssuerWellKnownProviderTest.java

@@ -75,6 +75,7 @@ import static org.keycloak.jose.jwe.JWEConstants.A256GCM;
 import static org.keycloak.jose.jwe.JWEConstants.RSA_OAEP;
 import static org.keycloak.jose.jwe.JWEConstants.RSA_OAEP_256;
 import static org.keycloak.protocol.oid4vc.issuance.OID4VCIssuerWellKnownProvider.ATTR_ENCRYPTION_REQUIRED;
+import org.keycloak.constants.Oid4VciConstants;
 
 
 public class OID4VCIssuerWellKnownProviderTest extends OID4VCIssuerEndpointTest {
@@ -83,7 +84,7 @@ public class OID4VCIssuerWellKnownProviderTest extends OID4VCIssuerEndpointTest
     public void configureTestRealm(RealmRepresentation testRealm) {
         Map<String, String> attributes = Optional.ofNullable(testRealm.getAttributes()).orElseGet(HashMap::new);
         attributes.put("credential_response_encryption.encryption_required", "true");
-        attributes.put("batch_credential_issuance.batch_size", "10");
+        attributes.put(Oid4VciConstants.BATCH_CREDENTIAL_ISSUANCE_BATCH_SIZE, "10");
         attributes.put("signed_metadata", "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIifQ.XYZ123abc");
         attributes.put(ATTR_ENCRYPTION_REQUIRED, "true");
         testRealm.setAttributes(attributes);
@@ -190,7 +191,7 @@ public class OID4VCIssuerWellKnownProviderTest extends OID4VCIssuerEndpointTest
         RealmModel realm = session.getContext().getRealm();
 
         realm.setAttribute(ATTR_ENCRYPTION_REQUIRED, "true");
-        realm.setAttribute("batch_credential_issuance.batch_size", "10");
+        realm.setAttribute(Oid4VciConstants.BATCH_CREDENTIAL_ISSUANCE_BATCH_SIZE, "10");
         realm.setAttribute("signed_metadata", "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJmb28iOiJiYXIifQ.XYZ123abc");
 
         OID4VCIssuerWellKnownProvider provider = new OID4VCIssuerWellKnownProvider(session);
@@ -413,6 +414,57 @@ public class OID4VCIssuerWellKnownProviderTest extends OID4VCIssuerEndpointTest
                 }));
     }
 
+    @Test
+    public void testBatchCredentialIssuanceValidation() {
+        KeycloakTestingClient testingClient = this.testingClient;
+
+        // Valid batch size (2 or greater) should be accepted
+        testBatchSizeValidation(testingClient, "5", true, 5);
+
+        // Invalid batch size (less than 2) should be rejected
+        testBatchSizeValidation(testingClient, "1", false, null);
+
+        // Edge case - batch size exactly 2 should be accepted
+        testBatchSizeValidation(testingClient, "2", true, 2);
+
+        // Zero batch size should be rejected
+        testBatchSizeValidation(testingClient, "0", false, null);
+
+        // Negative batch size should be rejected
+        testBatchSizeValidation(testingClient, "-1", false, null);
+
+        // Large valid batch size should be accepted
+        testBatchSizeValidation(testingClient, "1000", true, 1000);
+
+        // Non-numeric value should be rejected (parsing exception)
+        testBatchSizeValidation(testingClient, "invalid", false, null);
+    }
+
+    private void testBatchSizeValidation(KeycloakTestingClient testingClient, String batchSize, boolean shouldBePresent, Integer expectedValue) {
+        testingClient
+                .server(TEST_REALM_NAME)
+                .run(session -> {
+                    // Create a new isolated realm for testing
+                    RealmModel testRealm = session.realms().createRealm("test-batch-validation-" + batchSize);
+
+                    try {
+                        testRealm.setAttribute(Oid4VciConstants.BATCH_CREDENTIAL_ISSUANCE_BATCH_SIZE, batchSize);
+
+                        CredentialIssuer.BatchCredentialIssuance result = OID4VCIssuerWellKnownProvider.getBatchCredentialIssuance(testRealm);
+
+                        if (shouldBePresent) {
+                            Assert.assertNotNull("batch_credential_issuance should be present for batch size " + batchSize, result);
+                            Assert.assertEquals("batch_credential_issuance should have correct batch size for " + batchSize,
+                                    expectedValue, result.getBatchSize());
+                        } else {
+                            Assert.assertNull("batch_credential_issuance should be null for invalid batch size " + batchSize, result);
+                        }
+                    } finally {
+                        session.realms().removeRealm(testRealm.getId());
+                    }
+                });
+    }
+
     public static void extendConfigureTestRealm(RealmRepresentation testRealm, ClientRepresentation clientRepresentation) {
         if (testRealm.getComponents() == null) {
             testRealm.setComponents(new MultivaluedHashMap<>());