Migrate docs to antora

- First step of migration to antora by creating a structure
  which can be build locally.
- From docs to spring-security-kerberos-docs
- Gradle build handles needed docs logic, etc
- Relates #166

spring-security-kerberos-docs/modules/ROOT/examples/KerberosLdapContextSourceConfig.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2015 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
+ *
+ * http://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.kerberos.client.docs;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.core.io.FileSystemResource;
+import org.springframework.security.kerberos.client.config.SunJaasKrb5LoginConfig;
+import org.springframework.security.kerberos.client.ldap.KerberosLdapContextSource;
+import org.springframework.security.ldap.search.FilterBasedLdapUserSearch;
+import org.springframework.security.ldap.userdetails.LdapUserDetailsMapper;
+import org.springframework.security.ldap.userdetails.LdapUserDetailsService;
+
+public class KerberosLdapContextSourceConfig {
+
+//tag::snippetA[]
+	@Value("${app.ad-server}")
+	private String adServer;
+
+	@Value("${app.service-principal}")
+	private String servicePrincipal;
+
+	@Value("${app.keytab-location}")
+	private String keytabLocation;
+
+	@Value("${app.ldap-search-base}")
+	private String ldapSearchBase;
+
+	@Value("${app.ldap-search-filter}")
+	private String ldapSearchFilter;
+
+	@Bean
+	public KerberosLdapContextSource kerberosLdapContextSource() {
+		KerberosLdapContextSource contextSource = new KerberosLdapContextSource(adServer);
+		SunJaasKrb5LoginConfig loginConfig = new SunJaasKrb5LoginConfig();
+		loginConfig.setKeyTabLocation(new FileSystemResource(keytabLocation));
+		loginConfig.setServicePrincipal(servicePrincipal);
+		loginConfig.setDebug(true);
+		loginConfig.setIsInitiator(true);
+		contextSource.setLoginConfig(loginConfig);
+		return contextSource;
+	}
+
+	@Bean
+	public LdapUserDetailsService ldapUserDetailsService() {
+		FilterBasedLdapUserSearch userSearch =
+				new FilterBasedLdapUserSearch(ldapSearchBase, ldapSearchFilter, kerberosLdapContextSource());
+		LdapUserDetailsService service = new LdapUserDetailsService(userSearch);
+		service.setUserDetailsMapper(new LdapUserDetailsMapper());
+		return service;
+	}
+//end::snippetA[]
+
+}