People use Acegi 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 Acegi Security overcomes these problems, and also brings you dozens of other useful, entirely customisable security features.
As you probably know, security comprises two major operations. The first is known as "authentication", which 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 in 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 Acegi Security.
At an authentication level, Acegi 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, Acegi Security provides its own set of authentication features. Specifically, Acegi Security currently supports authentication with all of these technologies:
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HTTP BASIC authentication headers (an IEFT RFC-based standard)
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HTTP Digest authentication headers (an IEFT RFC-based standard)
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HTTP X.509 client certificate exchange (an IEFT RFC-based standard)
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LDAP (a very common approach to cross-platform authentication needs, especially in large environments)
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Form-based authentication (for simple user interface needs)
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Computer Associates Siteminder
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JA-SIG Central Authentication Service (otherwise known as CAS, which is a popular open source single sign on system)
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Transparent authentication context propagation for Remote Method Invocation (RMI) and HttpInvoker (a Spring remoting protocol)
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Automatic "remember-me" authentication (so you can tick a box to avoid re-authentication for a predetermined period of time)
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Anonymous authentication (allowing every call to automatically assume a particular security identity)
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Run-as authentication (which is useful if one call should proceed with a different security identity)
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Java Authentication and Authorization Service (JAAS)
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Container integration with JBoss, Jetty, Resin and Tomcat (so you can still use Container Manager Authentication if desired)
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Your own authentication systems (see below)
Many independent software vendors (ISVs) adopt Acegi Security because of this rich choice of 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, Acegi Security is an open platform and it is quite simple to write your own authentication mechanism. Many corporate users of Acegi Security need to integrate with "legacy" systems that don't follow any particular security standards, and Acegi 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. Or, you might want to ensure that an actual human being is making the requests and not some robot or other automated process. 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, Acegi Security fully supports automatic "channel security", together with JCaptcha integration for human user detection.
Irrespective of how authentication was undertaken, Acegi 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 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. Acegi Security provides deep capabilities in all of these important areas, which we'll explore later in this reference guide.
Source: Official Reference Guide
