# Introduction

## What is Spring Security?

Spring Security provides comprehensive security services for J2EE-based enterprise software applications. There is a particular emphasis on supporting projects built using The Spring Framework, which is the leading J2EE solution for enterprise software development. If you're not using Spring for developing enterprise applications, we warmly encourage you to take a closer look at it. Some familiarity with Spring - and in particular dependency injection principles - will help you get up to speed with Spring Security more easily.

People use Spring Security for many reasons, but most are drawn to the project after finding the security features of J2EE's Servlet Specification or EJB Specification lack the depth required for typical enterprise application scenarios. Whilst mentioning these standards, it's important to recognise that they are not portable at a WAR or EAR level. Therefore, if you switch server environments, it is typically a lot of work to reconfigure your application's security in the new target environment. Using Spring Security overcomes these problems, and also brings you dozens of other useful, customisable security features.

As you probably know two major areas of application security are authentication and authorization (or access-control). These are the two main areas that Spring Security targets. Authentication is the process of establishing a principal is who they claim to be (a principal generally means a user, device or some other system which can perform an action in your application). Authorization refers to the process of deciding whether a principal is allowed to perform an action within your application. To arrive at the point where an authorization decision is needed, the identity of the principal has already been established by the authentication process. These concepts are common, and not at all specific to Spring Security.

At an authentication level, Spring Security supports a wide range of authentication models. Most of these authentication models are either provided by third parties, or are developed by relevant standards bodies such as the Internet Engineering Task Force. In addition, Spring Security provides its own set of authentication features. Specifically, Spring Security currently supports authentication integration with all of these technologies:

- HTTP BASIC authentication headers (an IEFT RFC-based standard)

- HTTP Digest authentication headers (an IEFT RFC-based standard)

- HTTP X.509 client certificate exchange (an IEFT RFC-based standard)

- LDAP (a very common approach to cross-platform authentication needs, especially in large environments)

- Form-based authentication (for simple user interface needs)

- OpenID authentication

- Authentication based on pre-established request headers (such as Computer Associates Siteminder)

- JA-SIG Central Authentication Service (otherwise known as CAS, which is a popular open source single sign on system)

- Transparent authentication context propagation for Remote Method Invocation (RMI) and HttpInvoker (a Spring remoting protocol)

- Automatic "remember-me" authentication (so you can tick a box to avoid re-authentication for a predetermined period of time)

- Anonymous authentication (allowing every call to automatically assume a particular security identity)

- Run-as authentication (which is useful if one call should proceed with a different security identity)

- Java Authentication and Authorization Service (JAAS)

- JEE container autentication (so you can still use Container Managed Authentication if desired)

- Kerberos

- Java Open Source Single Sign On (JOSSO) *

- OpenNMS Network Management Platform *

- AppFuse *

- AndroMDA *

- Mule ESB *

- Direct Web Request (DWR) *

- Grails *

- Tapestry *

- JTrac *

- Jasypt *

- Roller *

- Elastic Path *

- Atlassian Crowd *

- Your own authentication systems (see below)

(* Denotes provided by a third party; check our integration page for links to the latest details)

Many independent software vendors (ISVs) adopt Spring Security because of this significant choice of flexible authentication models. Doing so allows them to quickly integrate their solutions with whatever their end clients need, without undertaking a lot of engineering or requiring the client to change their environment. If none of the above authentication mechanisms suit your needs, Spring Security is an open platform and it is quite simple to write your own authentication mechanism. Many corporate users of Spring Security need to integrate with "legacy" systems that don't follow any particular security standards, and Spring Security is happy to "play nicely" with such systems.

Sometimes the mere process of authentication isn't enough. Sometimes you need to also differentiate security based on the way a principal is interacting with your application. For example, you might want to ensure requests only arrive over HTTPS, in order to protect passwords from eavesdropping or end users from man-in-the-middle attacks. This is especially helpful to protect password recovery processes from brute force attacks, or simply to make it harder for people to duplicate your application's key content. To help you achieve these goals, Spring Security fully supports automatic "channel security", together with JCaptcha integration for human user detection.

Irrespective of how authentication was undertaken, Spring Security provides a deep set of authorization capabilities. There are three main areas of interest in respect of authorization, these being authorizing web requests, authorizing whether methods can be invoked, and authorizing access to individual domain object instances. To help you understand the differences, consider the authorization capabilities found in the Servlet Specification web pattern security, EJB Container Managed Security and file system security respectively. Spring Security provides deep capabilities in all of these important areas, which we'll explore later in this reference guide.

## History

Spring Security began in late 2003 as The Acegi Security System for Spring. A question was posed on the Spring Developers' mailing list asking whether there had been any consideration given to a Spring-based security implementation. At the time the Spring community was relatively small (especially compared with the size today!), and indeed Spring itself had only existed as a SourceForge project from early 2003. The response to the question was that it was a worthwhile area, although a lack of time currently prevented its exploration.

With that in mind, a simple security implementation was built and not released. A few weeks later another member of the Spring community inquired about security, and at the time this code was offered to them. Several other requests followed, and by January 2004 around twenty people were using the code. These pioneering users were joined by others who suggested a SourceForge project was in order, which was duly established in March 2004.

In those early days, the project didn't have any of its own authentication modules. Container Managed Security was relied upon for the authentication process, with Acegi Security instead focusing on authorization. This was suitable at first, but as more and more users requested additional container support, the fundamental limitation of container-specific authentication realm interfaces became clear. There was also a related issue of adding new JARs to the container's classpath, which was a common source of end user confusion and misconfiguration.

Acegi Security-specific authentication services were subsequently introduced. Around a year later, Acegi Security became an official Spring Framework subproject. The 1.0.0 final release was published in May 2006 - after more than two and a half years of active use in numerous production software projects and many hundreds of improvements and community contributions.

Acegi Security became an official Spring Portfolio project towards the end of 2007 and was rebranded as Spring Security.

Today Spring Security enjoys a strong and active open source community. There are thousands of messages about Spring Security on the support forums. There is an active core of developers who work on the code itself and an active community which also regularly share patches and support their peers.

## Release Numbering

It is useful to understand how Spring Security release numbers work, as it will help you identify the effort (or lack thereof) involved in migrating to future releases of the project. Officially, we use the Apache Portable Runtime Project versioning guidelines, which can be viewed at `http://apr.apache.org/versioning.html`. We quote the introduction contained on that page for your convenience:

Versions are denoted using a standard triplet of integers: MAJOR.MINOR.PATCH. The basic intent is that MAJOR versions are incompatible, large-scale upgrades of the API. MINOR versions retain source and binary compatibility with older minor versions, and changes in the PATCH level are perfectly compatible, forwards and backwards.

## Getting Spring Security

You can get hold of Spring Security in several ways. You can download a packaged distribution from the main Spring download page, download individual jars (and sample WAR files) from the Maven Central repository (or a SpringSource Maven repository for snapshot and milestone releases) or, alternatively, you can build the project from source yourself. See the project web site for more details.

### Project Modules

In Spring Security 3.0, the codebase has been sub-divided into separate jars which more clearly separate different functionaltiy areas and third-party dependencies. If you are using Maven to build your project, then these are the modules you will add to your `pom.xml`. Even if you're not using Maven, we'd recommend that you consult the `pom.xml` files to get an idea of third-party dependencies and versions. Alternatively, a good idea is to examine the libraries that are included in the sample applications.

#### Core - `spring-security-core.jar`

Contains core authentication and access-contol classes and interfaces, remoting support and basic provisioning APIs. Required by any application which uses Spring Security. Supports standalone applications, remote clients, method (service layer) security and JDBC user provisioning. Contains the top-level packages:

- `org.springframework.security.core`

- `org.springframework.security.access`

- `org.springframework.security.authentication`

- `org.springframework.security.provisioning`

- `org.springframework.security.remoting`

#### Web - `spring-security-web.jar`

Contains filters and related web-security infrastructure code. Anything with a servlet API dependency. You'll need it if you require Spring Security web authentication services and URL-based access-control. The main package is `org.springframework.security.web`.

#### Config - `spring-security-config.jar`

Contains the security namespace parsing code. You need it if you are using the Spring Security XML namespace for configuration. The main package is `org.springframework.security.config`. None of the classes are intended for direct use in an application.

#### LDAP - `spring-security-ldap.jar`

LDAP authentication and provisioning code. Required if you need to use LDAP authentication or manage LDAP user entries. The top-level package is `org.springframework.security.ldap`.

#### ACL - `spring-security-acl.jar`

Specialized domain object ACL implementation. Used to apply security to specific domain object instances within your application. The top-level package is `org.springframework.security.acls`.

#### CAS - `spring-security-cas-client.jar`

Spring Security's CAS client integration. If you want to use Spring Security web authentication with a CAS single sign-on server. The top-level package is `org.springframework.security.cas`.

#### OpenID - `spring-security-openid.jar`

OpenID web authentication support. Used to authenticate users against an external OpenID server. `org.springframework.security.openid`. Requires OpenID4Java.

### Checking out the Source

Since Spring Security is an Open Source project, we'd strongly encourage you to check out the source code using git. This will give you full access to all the sample applications and you can build the most up to date version of the project easily. Having the source for a project is also a huge help in debugging. Exception stack traces are no longer obscure black-box issues but you can get straight to the line that's causing the problem and work out what's happening. The source is the ultimate documentation for a project and often the simplest place to find out how something actually works.

To obtain the source for the project trunk, use the following git command:

      git clone git://git.springsource.org/spring-security/spring-security.git

You can checkout specific versions from `https://src.springframework.org/svn/spring-security/tags/`.