////
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you 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.
////

[[core-x509]]
=== Certificate (X.509) Login Authentication

Another authentication mechanism supported by Spring Security is certificate-based, or "`mutual authentication`". It requires HTTPS, and you must configure the server to require a client certificate (ordinarily only the server provides a certificate). Your username is extracted from the client certificate if it is valid, and you are "`pre-authenticated`". As long as a corresponding username exists in the database, your authentication succeeds and you are not asked for a password. Your `Authentication` contains the authorities associated with your username.

The table describes available configuration options.

.X.509 configuration options
[cols="30,30,40"]
|====================
| *Property* | *Default Value* | *Meaning*

|useX509
|`false`
|Whether to support certificate-based logins

|x509.continueFilterChainOnUnsuccessfulAuthentication
|`true`
|Whether to proceed when an authentication attempt fails to allow other authentication mechanisms to process the request

|x509.subjectDnRegex
|"`CN=(.*?)(?:,\|$)`"
|Regular expression for extracting the username from the certificate's subject name

|x509.checkForPrincipalChanges
|`false`
|Whether to re-extract the username from the certificate and check that it's still the current user when a valid `Authentication` already exists

|x509.invalidateSessionOnPrincipalChange
|`true`
|Whether to invalidate the session if the principal changed (based on a `checkForPrincipalChanges` check)

|x509.subjectDnClosure
|_none_
|If set, the plugin's `ClosureX509PrincipalExtractor` class is used to extract information from the X.509 certificate using the specified closure

|x509.throwExceptionWhenTokenRejected
|`false`
|If `true` thrown a `BadCredentialsException`
|====================

The details of configuring your server for SSL and configuring browser certificates are beyond the scope of this document. If you use Tomcat, see its https://tomcat.apache.org/tomcat-8.0-doc/ssl-howto.html[SSL documentation]. To get a test environment working, see the instructions in https://stackoverflow.com/q/1180397/160313[this discussion at Stack Overflow].
