fix: make Saml2Authentication serializable

saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/OpenSamlAuthenticationProvider.java

@@ -178,7 +178,7 @@ public final class OpenSamlAuthenticationProvider implements AuthenticationProvi
 			Assertion assertion = validateSaml2Response(token, token.getRecipientUri(), samlResponse);
 			String username = getUsername(token, assertion);
 			return new Saml2Authentication(
-					() -> username, token.getSaml2Response(),
+					new SimpleSaml2AuthenticatedPrincipal(username), token.getSaml2Response(),
 					this.authoritiesMapper.mapAuthorities(getAssertionAuthorities(assertion))
 			);
 		} catch (Saml2AuthenticationException e) {

saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/Saml2AuthenticatedPrincipal.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2002-2019 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.saml2.provider.service.authentication;
+
+import org.springframework.security.core.AuthenticatedPrincipal;
+
+/**
+ * Saml2 representation of an {@link AuthenticatedPrincipal}.
+ *
+ * @author Clement Stoquart
+ * @since 5.3
+ */
+public interface Saml2AuthenticatedPrincipal extends AuthenticatedPrincipal {
+}

saml2/saml2-service-provider/src/main/java/org/springframework/security/saml2/provider/service/authentication/SimpleSaml2AuthenticatedPrincipal.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2002-2019 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.saml2.provider.service.authentication;
+
+import java.io.Serializable;
+
+/**
+ * Default implementation of a {@link Saml2AuthenticatedPrincipal}.
+ *
+ * @author Clement Stoquart
+ * @since 5.3
+ */
+class SimpleSaml2AuthenticatedPrincipal implements Saml2AuthenticatedPrincipal, Serializable {
+
+	private final String name;
+
+	SimpleSaml2AuthenticatedPrincipal(String name) {
+		this.name = name;
+	}
+
+	@Override
+	public String getName() {
+		return this.name;
+	}
+}

saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/OpenSamlAuthenticationProviderTests.java

@@ -16,6 +16,10 @@
 
 package org.springframework.security.saml2.provider.service.authentication;
 
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutputStream;
+
 import org.springframework.security.core.Authentication;
 
 import org.hamcrest.BaseMatcher;
@@ -346,6 +350,28 @@ public class OpenSamlAuthenticationProviderTests {
 		provider.authenticate(token);
 	}
 
+	@Test
+	public void writeObjectWhenTypeIsSaml2AuthenticationThenNoException() throws IOException {
+		Response response = response(recipientUri, idpEntityId);
+		Assertion assertion = defaultAssertion();
+		signXmlObject(
+				assertion,
+				assertingPartyCredentials(),
+				recipientEntityId
+		);
+		EncryptedAssertion encryptedAssertion = encryptAssertion(assertion, assertingPartyCredentials());
+		response.getEncryptedAssertions().add(encryptedAssertion);
+		token = responseXml(response, idpEntityId);
+
+		Saml2Authentication authentication = (Saml2Authentication) provider.authenticate(token);
+
+		// the following code will throw an exception if authentication isn't serializable
+		ByteArrayOutputStream byteStream = new ByteArrayOutputStream(1024);
+		ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteStream);
+		objectOutputStream.writeObject(authentication);
+		objectOutputStream.flush();
+	}
+
 	private Assertion defaultAssertion() {
 		return assertion(
 				username,

saml2/saml2-service-provider/src/test/java/org/springframework/security/saml2/provider/service/authentication/SimpleSaml2AuthenticatedPrincipalTests.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2002-2019 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.saml2.provider.service.authentication;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class SimpleSaml2AuthenticatedPrincipalTests {
+
+	@Test
+	public void createSimpleSaml2AuthenticatedPrincipal() {
+		SimpleSaml2AuthenticatedPrincipal principal = new SimpleSaml2AuthenticatedPrincipal("user");
+
+		Assert.assertEquals("user", principal.getName());
+	}
+}