Add Jackson Support for Saml2 Module

Closes gh-10905

core/src/test/java/org/springframework/security/jackson2/UnmodifiableMapDeserializerTests.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.security.jackson2;
+
+import java.util.Collections;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+import org.skyscreamer.jsonassert.JSONAssert;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class UnmodifiableMapDeserializerTests extends AbstractMixinTests {
+
+	// @formatter:off
+	private static final String DEFAULT_MAP_JSON = "{"
+			+ "\"@class\": \"java.util.Collections$UnmodifiableMap\","
+			+ "\"Key\": \"Value\""
+			+ "}";
+	// @formatter:on
+
+	@Test
+	void shouldSerialize() throws Exception {
+		String mapJson = mapper
+				.writeValueAsString(Collections.unmodifiableMap(Collections.singletonMap("Key", "Value")));
+
+		JSONAssert.assertEquals(DEFAULT_MAP_JSON, mapJson, true);
+	}
+
+	@Test
+	void shouldDeserialize() throws Exception {
+		Map<String, String> map = mapper.readValue(DEFAULT_MAP_JSON,
+				Collections.unmodifiableMap(Collections.emptyMap()).getClass());
+
+		assertThat(map).isNotNull().isInstanceOf(Collections.unmodifiableMap(Collections.emptyMap()).getClass())
+				.containsAllEntriesOf(Map.of("Key", "Value"));
+	}
+
+}