Set anonymousReadOnly true when userDn is not provided

Fixes spring-projectsgh-473

core/src/main/java/org/springframework/ldap/core/support/AbstractContextSource.java

@@ -413,6 +413,7 @@ public void afterPropertiesSet() {
 			LOG.debug("AuthenticationSource not set - " + "using default implementation");
 			if (!StringUtils.hasText(userDn)) {
 				LOG.info("Property 'userDn' not set - " + "anonymous context will be used for read-write operations");
+				anonymousReadOnly = true;
 			}
 			else if (!StringUtils.hasText(password)) {
 				LOG.info("Property 'password' not set - " + "blank password will be used");

test/integration-tests/src/test/java/org/springframework/ldap/itest/ldap473/Ldap473Test.java

@@ -0,0 +1,61 @@
+package org.springframework.ldap.itest.ldap473;
+
+import javax.naming.directory.DirContext;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.ldap.core.ContextSource;
+import org.springframework.ldap.core.support.LdapContextSource;
+import org.springframework.ldap.test.EmbeddedLdapServerFactoryBean;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Eddú Meléndez
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+public class Ldap473Test {
+
+	@Autowired
+	private ContextSource contextSource;
+
+	@Test
+	public void anonymous() {
+		DirContext readOnlyContext = contextSource.getReadOnlyContext();
+		assertThat(readOnlyContext).isNotNull();
+	}
+
+	@Configuration
+	static class ContextSourceConfig {
+
+		@Bean
+		public ContextSource contextSource() {
+			LdapContextSource contextSource = new LdapContextSource();
+			contextSource.setUrl("ldap://localhost:9321");
+			contextSource.setUserDn(null);
+			contextSource.setPassword(null);
+			return contextSource;
+		}
+
+	}
+
+	@Configuration
+	static class EmbeddedLdapConfig {
+
+		@Bean
+		public EmbeddedLdapServerFactoryBean embeddedLdapServer() {
+			EmbeddedLdapServerFactoryBean embeddedLdapServer = new EmbeddedLdapServerFactoryBean();
+			embeddedLdapServer.setPartitionName("example");
+			embeddedLdapServer.setPartitionSuffix("dc=261consulting,dc=com");
+			embeddedLdapServer.setPort(9321);
+			return embeddedLdapServer;
+		}
+
+	}
+
+}