Do not request unnecessary LDAP attributes

src/main/java/de/thm/arsnova/config/SecurityConfig.java

@@ -274,6 +274,7 @@ public class SecurityConfig extends WebSecurityConfigurerAdapter implements Serv
 	@Bean
 	public LdapAuthenticator ldapAuthenticator() throws Exception {
 		BindAuthenticator authenticator = new BindAuthenticator(ldapContextSource());
+		authenticator.setUserAttributes(new String[] {ldapUserIdAttr});
 		if (!"".equals(ldapSearchFilter)) {
 			logger.debug("ldapSearch: {} {}", ldapSearchBase, ldapSearchFilter);
 			authenticator.setUserSearch(new FilterBasedLdapUserSearch(ldapSearchBase, ldapSearchFilter, ldapContextSource()));