github
/
spring-security
zrcadlo https://github.com/spring-projects/spring-security


			
				
					
						
						
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<title>Frequently Asked Questions (FAQ) on Acegi Security</title>
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  <h1>Frequently Asked Questions</h1>
  
  <h2>What is Acegi Security?</h2>
  <p>Acegi Security is an open source project that provides comprehensive authentication
	and authorisation services for enterprise applications based on
	<a href="http://www.springframework.org">The Spring Framework</a>.
	Acegi Security can authenticate using a variety of pluggable providers, and
	can authorise both web requests and method invocations.
	Acegi Security provides an integrated security approach across
	these various targets, and also offers access control list (ACL) capabilities to
	enable individual domain object instances to be secured. At an implementation
	level, Acegi Security is managed through Spring's inversion of control and 
	lifecycle services,	and actually enforces security using interception through
	servlet Filters and Java AOP frameworks. In terms of AOP framework support, Acegi
	Security currently supports AOP Alliance (which is what the
	Spring IoC container uses internally) and AspectJ, although additional frameworks
	can be easily supported.</p>

  <h2>Why not just use web.xml security?</h2>
  <p>Let's assume you're developing an enterprise application based on Spring.
	There are four security concerns you typically need to address: authentication,
	web request security, service layer security (ie your methods that implement
	business logic), and domain object instance security (ie different domain objects
	have different permissions). With these typical requirements in mind:
	<ol>
		<li><b>Authentication</b>: The servlet specification provides an approach
			to authentication. However, you will need to configure the container 
			to perform authentication which typically requires editing of
			container-specific "realm" settings. This makes a non-portable
			configuration, and if you need to write an actual Java class to implement 
			the container's authentication interface, it becomes even more non-portable.
			With Acegi Security you achieve complete portability - right down to the 
			WAR level. Also, Acegi Security offers a choice of production-proven
			authentication providers and mechanisms, meaning you can switch your 
			authentication approaches at deployment time. This is particularly
			valuable for software vendors writing products that need to work in
			an unknown target environment.<br><br></li>
		<li><b>Web request security:</b> The servlet specification provides an
			approach to secure your request URIs. However, these URIs can only be
			expressed in the servlet specification's own limited URI path format.
			Acegi Security provides a far more comprehensive approach. For instance,
			you can use Ant paths or regular expressions, you can consider parts of the
			URI other than simply the requested page (eg you can consider HTTP GET
			parameters), and you can implement your own runtime source of configuration
			data. This means your web request security can be dynamically changed during
			the actual execution of your webapp.<br><br></li>
		<li><b>Service layer and domain object security:</b> The absence of support 
			in the servlet specification for services layer security or domain object 
			instance security represent serious limitations for multi-tiered 
			applications. Typically developers either ignore these requirements, or
			implement security logic within their MVC controller code (or even worse,
			inside the views). There are serious disadvantages with this approach:<br><br>
				<ol>
					<li><i>Separation of concerns:</i> Authorization is a 
						crosscutting concern and should be implemented as such. 
						MVC controllers or views implementing authorization code 
						makes it more difficult to test both the controller and 
						authorization logic, more difficult to debug, and will 
						often lead to code duplication.</li>
					<li><i>Support for rich clients and web services:</i> If an 
						additional client type must ultimately be supported, any 
						authorization code embedded within the web layer is 
						non-reusable. It should be considered that Spring remoting 
						exporters only export service layer beans (not MVC 
						controllers). As such authorization logic needs to be 
						located in the services layer to support a multitude of 
						client types.</li>
					<li><i>Layering issues:</i> An MVC controller or view is simply 
						the incorrect architectural layer to implement authorization 
						decisions concerning services layer methods or domain object 
						instances. Whilst the Principal may be passed to the services 
						layer to enable it to make the authorization decision, doing 
						so would introduce an additional argument on every services 
						layer method. A more elegant approach is to use a ThreadLocal 
						to hold the Principal, although this would likely increase 
						development time to a point where it would become more
						economical (on a cost-benefit basis) to simply use a dedicated 
						security framework.</li>
					<li><i>Authorisation code quality:</i> It is often said of web 
						frameworks that they "make it easier to do the right things, 
						and harder to do the wrong things". Security frameworks are 
						the same, because they are designed in an abstract manner for 
						a wide range of purposes. Writing your own authorization code 
						from scratch does not provide the "design check" a framework 
						would offer, and in-house authorization code will typically 
						lack the improvements that emerge from widespread deployment, 
						peer review and new versions.
				</ol>
				</li>
	</ol>
	For simple applications, servlet specification security may just be enough.
	Although when considered within the context of web container portability, 
	configuration requirements, limited web request security flexibility, and 
	non-existent services layer and domain object instance security, it becomes 
	clear why developers often look to alternative solutions.
	</p>

  <h2>How do you pronounce "Acegi"?</h2>
  <p><i>Ah-see-gee</i>. Said quickly, without emphasis on any part.
	Acegi isn't an acronym, name of a Greek God or anything similarly
	impressive - it's just letters #1, #3, #5, #7 and #9 of the alphabet.</p>

  <h2>Is it called "Acegi" or "Acegi Security"?</h2>
  <p>It's official name is <i>Acegi Security System for Spring</i>,
	although we're happy for it to be abbreviated to
	<i>Acegi Security</i>. Please don't just call it <i>Acegi</i>, though,
	as that gets confused with the name of the company that maintains Acegi
	Security.</p>

  <h2>What catches 80% of users reporting problems?</h2>
  <p>80% of support questions are because people have not defined
	the necessary filters in <code>web.xml</code>, or the filters are being
	mapped in the incorrect order. Check the 
	<a href="reference.html">Reference Guide</a>, which
	has a specific section on filter ordering.</p>
  
  <h2>I'm sure my filters are ordered correctly. What else could be wrong?</h2>
  <p>The next most common source of problems stem from custom
	<code>AuthenticationDao</code> implementations that simply don't properly
	implement the interface contract. For example, they return <code>null</code> instead
	of the user not found exception, or fail to add in the
	<code>GrantedAuthority[]</code>s. Whilst <code>DaoAuthenticationProvider</code>
	does its best to check the <code>AuthenticationDao</code> returns a valid 
	<code>UserDetails</code>, we suggest you write the
	<code>UserDetails</code> object to the log and check it looks correct.</p>

  <h2>I need some help. What files should I post?</h2>
  <p>The most important things to post with any support requests on the
	<a href="http://forum.springframework.org">Spring Forums</a> are your
	<code>web.xml</code>, <code>applicationContext.xml</code> (or whichever
	XML loads the security-related beans) as well as any custom
	<code>AuthenticationDao</code> you might be using. For really odd problems,
	also switch on debug-level logging and include the resulting log.</p>

  <h2>How do I switch on debug-level logging?</h2>
  <p>Acegi Security uses Commons Logging, just as Spring does. So you use the
	same approach as you'd use for Spring. Most people output to Log4J, so
	the following <code>log4j.properties</code> would work:</p>
	
	<pre>
		log4j.rootCategory=WARN, stdout
		
		log4j.appender.stdout=org.apache.log4j.ConsoleAppender
		log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
		log4j.appender.stdout.layout.ConversionPattern=%d %p %c - %m%n
		
		log4j.category.net.sf.acegisecurity=DEBUG</pre>

  <h2>How do I store custom properties, like a user's email address?</h2>
  <p>In most cases write an <code>AuthenticationDao</code> which returns
	a subclass of <code>User</code>. Alternatively, write your own
	<code>UserDetails</code> implementation from scratch and return that.</p>

  <h2>Why doesn't Acegi Security use JAAS?</h2>
  <p>Acegi Security targets <i>enterprise applications</i>, which are typically
	multi-user, data-oriented applications that are important to
	the core business. Acegi Security was designed to provide a portable and effective
	security framework for this target application type. It was not designed for securing
	limited privilege runtime environments, such as web browser applets.</p>
	
	<p>We did consider JAAS when designing Acegi Security, but it simply
	wasn't suitable for our purpose. We needed to avoid complex JRE configurations,
	we needed container portability, and we wanted maximum leveraging of the Spring IoC
	container. Particularly as limited privilege runtime environments were not
	an actual requirement, this lead to the natural design of Acegi Security as
	it exists today.</p>
	
	<p>Acegi Security already provides some JAAS integration. It can today authenticate
	via delegation to a JAAS login module. This means it offers the same level of JAAS
	integration as many web containers. Indeed the container adapter model supported by
	Acegi Security allows Acegi Security and container-managed security to happily
	co-exist and benefit from each other. Any debate about Acegi Security and JAAS
	should therefore centre on the authorisation issue. An evaluation of major
	containers and security frameworks would reveal that Acegi Security is by no
	means unusual in not using JAAS for authorisation.</p>
	
	<p>There are many examples of open source applications being preferred to
	official standards. A few that come to mind in the Java community include
	using Spring managed POJOs (rather than EJBs), Hibernate (instead of entity beans),
	Log4J (instead of JDK logging), Tapestry (instead of JSF), and Velocity/FreeMarker
	(instead of JSP). It's important to recognise that many open source projects do
	develop into de facto standards, and in doing so play a legitimate and beneficial
	role in professional software development.</p>

  <h2>Do you welcome contributions?</h2>
  <p>Yes. If you've written something and it works well, please feel free to share it.
	Simply email the contribution to the 
	<a href="mail-lists.html">acegisecurity-developers</a> list. If you haven't yet
	written the contribution, we encourage you to send your thoughts to the same 
	list so that you can receive some initial design feedback.</p>
	
	<p>For a contribution to be used, it must have appropriate unit test coverage and
	detailed JavaDocs. It will ideally have some comments for the Reference Guide
	as well (this can be sent in word processor or HTML format if desired). This
	helps ensure the contribution maintains the same quality as the remainder of
	the project.</p>
	
	<p>We also welcome documentation improvements, unit tests, illustrations,
	people supporting the user community (especially on the forums), design ideas,
	articles, blog entries, presentations and alike. If you're looking for something
	to do, you can always email the
	<a href="mail-lists.html">acegisecurity-developers</a> list and we'll be
	pleased to suggest something. :-)</p>

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