2009-07-23 20:42:04 +00:00

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<?xml version="1.0" encoding="UTF-8"?>
<?oxygen RNGSchema="http://www.oasis-open.org/docbook/xml/5.0/rng/docbook.rng" type="xml"?>
<article class="faq" xml:id="spring-security-faq" xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"><info>
<title>Frequently Answered Questions (FAQ)</title>
</info>
<qandaset>
<qandadiv>
<title>General</title>
<qandaentry xml:id="faq-other-concerns">
<question>
<para>Will Spring Security take care of all my application security
requirements?</para>
</question>
<answer>
<para> Spring Security provides you with a very flexible framework for your
authentication and authorization requirements, but there are many other
considerations for building a secure application that are outside its scope.
Web applications are vulnerable to all kinds of attacks which you should be
familiar with, preferably before you start development so you can design and
code with them in mind from the beginning. Check out the <link
xlink:href="http://www.owasp.org/">OWASP web site</link> for information
on the major issues facing web application developers and the
countermeasures you can use against them.</para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-web-xml">
<question>
<para>Why not just use web.xml security?</para>
</question>
<answer>
<para>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 (i.e. your
methods that implement business logic), and domain object instance security
(i.e. different domain objects have different permissions). With these
typical requirements in mind: <orderedlist>
<listitem>
<para><emphasis>Authentication</emphasis>: 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 Spring Security you achieve complete portability - right
down to the WAR level. Also, Spring 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.</para>
</listitem>
<listitem>
<para><emphasis>Web request security:</emphasis> 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. Spring 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 (e.g. 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.</para>
</listitem>
<listitem>
<para><emphasis>Service layer and domain object security:</emphasis>
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: <orderedlist>
<listitem>
<para><emphasis>Separation of concerns:</emphasis>
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.</para>
</listitem>
<listitem>
<para><emphasis>Support for rich clients and web
services:</emphasis> 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.</para>
</listitem>
<listitem>
<para><emphasis>Layering issues:</emphasis> 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.</para>
</listitem>
<listitem>
<para><emphasis>Authorisation code quality:</emphasis>
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. </para>
</listitem>
</orderedlist></para>
</listitem>
</orderedlist></para>
<para> 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. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-requirements">
<question>
<para>What Java and Spring Framework versions are required?</para>
</question>
<answer>
<para> Spring Security 2.0.x requires a minimum JDK version of 1.4 and is built
against Spring 2.0.x. It should also be compatible with applications using
Spring 2.5.x. </para>
<para> Spring Security 3.0 requires JDK 1.5 as a minimum and will also require
Spring 3.0. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-start-simple">
<question>
<para> I'm new to Spring Security and I need to build an application that
supports CAS single sign-on over HTTPS, while allowing Basic authentication
locally for certain URLs, authenticating against multiple back end user
information sources (LDAP and JDBC). I've copied some configuration files I
found but it doesn't work. What could be wrong? </para>
<para>Or subsititute an alternative complex scenario...</para>
</question>
<answer>
<para> Realistically, you need an understanding of the technolgies you are
intending to use before you can successfully build applications with them.
Security is complicated. Setting up a simple configuration using a login
form and some hard-coded users using Spring Security's namespace is
reasonably straightforward. Moving to using a backed JDBC database is also
easy enough. But if you try and jump straight to a complicated deployment
scenario like this you will almost certainly be frustrated. There is a big
jump in the learning curve required to set up systems like CAS, configure
LDAP servers and install SSL certificates properly. So you need to take
things one step at a time. </para>
<para> From a Spring Security perspective, the first thing you should do is
follow the <quote>Getting Started</quote> guide on the web site. This will
take you through a series of steps to get up and running and get some idea
of how the framework operates. If you are using other technologies which you
aren't familiar with then you should do some research and try to make sure
you can use them in isolation before combining them in a complex system.
</para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<title>Common Problems</title>
<qandaentry xml:id="faq-login-loop">
<question>
<para>My application goes into an "endless loop" when I try to login, what's
going on?</para>
</question>
<answer>
<para>A common user problem with infinite loop and redirecting to the login page
is caused by accidently configuring the login page as a "secured" resource.
Make sure your configuration allows anonymous access to the login page,
either by excluding it from the security filter chain or marking it as
requiring ROLE_ANONYMOUS.</para>
<para>If your AccessDecisionManager includes an AutheticatedVoter, you can use
the attribute "IS_AUTHENTICATED_ANONYMOUSLY". This is automatically
available if you are using the standard namespace configuration setup. </para>
<para> From Spring Security 2.0.1 onwards, when you are using namespace-based
configuration, a check will be made on loading the application context and a
warning message logged if your login page appears to be protected. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-anon-access-denied">
<question>
<para>I get an exception with the message "Access is denied (user is
anonymous);". What's wrong?</para>
</question>
<answer>
<para> This is a debug level message which occurs the first time an anonymous
user attempts to access a protected resource.
<programlisting>
DEBUG [ExceptionTranslationFilter] - Access is denied (user is anonymous); redirecting to authentication entry point
org.springframework.security.AccessDeniedException: Access is denied
at org.springframework.security.vote.AffirmativeBased.decide(AffirmativeBased.java:68)
at org.springframework.security.intercept.AbstractSecurityInterceptor.beforeInvocation(AbstractSecurityInterceptor.java:262)
</programlisting>
It is normal and shouldn't be anything to worry about. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-cached-secure-page">
<question>
<para>Why can I still see a secured page even after I've logged out of my application?</para>
</question>
<answer>
<para>The most common reason for this is that your browser has cached the page and you are seeing a
copy which is being retrieved from the browsers cache. Verify this by checking whether the browser is actually sending
the request (check your server access logs, the debug log or use a suitable browser debugging plugin such as <quote>Tamper Data</quote>
for Firefox). This has nothing to do with Spring Security and you should configure your application or server to set the
appropriate <literal>Cache-Control</literal> response headers. Note that SSL requests are never cached.</para>
</answer>
</qandaentry>
<qandaentry xml:id="auth-exception-credentials-not-found">
<question>
<para>I get an exception with the message "An Authentication object was not
found in the SecurityContext". What's wrong?</para>
</question>
<answer>
<para> This is a another debug level message which occurs the first time an
anonymous user attempts to access a protected resource, but when you do not
have an AnonymousProcessingFilter in your filter chain configuration.
<programlisting>
DEBUG [ExceptionTranslationFilter] - Authentication exception occurred; redirecting to authentication entry point
org.springframework.security.AuthenticationCredentialsNotFoundException: An Authentication object was not found in the SecurityContext
at org.springframework.security.intercept.AbstractSecurityInterceptor.credentialsNotFound(AbstractSecurityInterceptor.java:342)
at org.springframework.security.intercept.AbstractSecurityInterceptor.beforeInvocation(AbstractSecurityInterceptor.java:254)
</programlisting>
It is normal and shouldn't be anything to worry about. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-tomcat-https-session">
<question>
<para> I'm using Tomcat and have enabled HTTPS for my login page, switching back
to HTTP afterwards. It doesn't work - I just end up back at the login page
after authenticating. </para>
</question>
<answer>
<para> This happens because Tomcat sessions created under HTTPS cannot
subsequently be used under HTTP and any session state is lost (including the
security context information). Starting a session in HTTP first should work
as the session cookie won't be marked as secure. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-no-security-on-forward">
<question>
<para> I'm forwarding a request to another URL using the RequestDispatcher, but
my security constraints aren't being applied. </para>
</question>
<answer>
<para> Filters are not applied by default to forwards or includes. If you really
want the security filters to be applied to forwards and/or includes, then
you have to configure these explicitly in your web.xml using the
&lt;dispatcher&gt; element, a child element of &lt;filter-mapping&gt;.
</para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-session-listener-missing">
<question>
<para> I'm trying to use the concurrent session-control support but it won't let
me log back in, even if I'm sure I've logged out and haven't exceeded the
allowed sessions. </para>
</question>
<answer>
<para>Make sure you have added the listener to your web.xml file. It is
essential to make sure that the Spring Security session registry is notified
when a session is destroyed. Without it, the session information will not be
removed from the registry.</para>
<programlisting><![CDATA[
<listener>
<listener-class>org.springframework.security.ui.session.HttpSessionEventPublisher</listener-class>
</listener> ]]>
</programlisting>
</answer>
</qandaentry>
<qandaentry xml:id="faq-no-filters-no-context">
<question>
<para>I have a user who has definitely been authenticated, but when I try to
access the <classname>SecurityContextHolder</classname> during some
requests, the <interfacename>Authentication</interfacename> is null. Why
can't I see the user information? </para>
</question>
<answer>
<para>If you have excluded the request from the security filter chain using the
attribute <literal>filters='none'</literal> in the
<literal>&lt;intercept-url></literal> element that matches the URL
pattern, then the <classname>SecurityContextHolder</classname> will not be
populated for that request. Check the debug log to see whether the request
is passing through the filter chain. (You are reading the debug log,
right?).</para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-method-security-in-web-context">
<question><para>I have added Spring Security's &lt;global-method-security&gt; element to my application context but if I add
security annotations to my Spring MVC controller beans (Struts actions etc.) then they don't seem to have an effect.</para>
</question>
<answer><para>
The application context which holds the Spring MVC beans for the dispatcher servlet is a child application context
of the main application context which is loaded using the <classname>ContextLoaderListener</classname> you define in your
<filename>web.xml</filename>. The beans in the child context are not visible in the parent context so you need to either
move the &lt;global-method-security&gt; declaration to the web context or moved the beans you want secured into the main
application context.
</para>
<para>Generally we would recommend applying method security at the service layer rather than on individual web
controllers.</para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<title>Spring Security Architecture Questions</title>
<qandaentry xml:id="faq-where-is-class-x">
<question>
<para>How do I know which package class X is in?</para>
</question>
<answer>
<para>The best way of locating classes is by installing the Spring Security
source in your IDE. The distribution includes source jars for each of the
modules the project is divided up into. Add these to your project source
path and you can navigate directly to Spring Security classes
(<command>Ctrl-Shift-T</command> in Eclipse). This also makes debugging
easer and allows you to troubleshoot exceptions by looking directly at the
code where they occur to see what's going on there. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-namespace-to-bean-mapping">
<question>
<para>How do the namespace elements map to conventional bean
configurations?</para>
</question>
<answer>
<para>There is a general overview of what beans are created by the namespace in
the namespace appendix of the reference guide. If want to know the full
details then the code is in the <filename>spring-security-config</filename>
module within the Spring Security 3.0 distribution. You should probably read
the chapters on namespace parsing in the standard Spring Framework reference
documentation first. </para>
</answer>
</qandaentry>
</qandadiv>
<qandadiv>
<title>Common <quote>Howto</quote> Requests</title>
<qandaentry xml:id="faq-extra-login-fields">
<question>
<para>I need to login in with more information than just the username. How do I
add support for extra login fields (e.g. a company name)?</para>
</question>
<answer>
<para>This question comes up repeatedly in the Spring Security forum so you will
find more information there by searching the archives (or through
google).</para>
<para> The submitted login information is processed by an instance of
<classname>AuthenticationProcessingFilter</classname>. You will need to
customize this class to handle the extra data field(s). One option is to use
your own customized authentication token class (rather than the standard
<classname>UsernamePasswordAuthenticationToken</classname>), another is
simply to concatenate the extra fields with the username (for example, using
a ":" as the separator) and pass them in the username property of
<classname>UsernamePasswordAuthenticationToken</classname>. </para>
<para> You will also need to customize the actual authentication process. If you
are using a custom authentication token class, for example, you will have to
write an <classname>AuthenticationProvider</classname> to handle it (or
extend the standard <classname>DaoAuthenticationProvider</classname>). If
you have concatenated the fields, you can implement your own
<interfacename>UserDetailsService</interfacename> which splits them up
and loads the appropriate user data for authentication. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-dynamic-url-metadata">
<question>
<para>How do I define the secured URLs within an application
dynamically?</para>
</question>
<answer>
<para>People often ask about how to store the mapping between secured URLs and
security metadata attributes in a database, rather than in the application
context. </para>
<para> The first thing you should ask yourself is if you really need to do this.
If an application requires securing, then it also requires that the security
be tested thoroughly based on a defined policy. It may require auditing and
acceptance testing before being rolled out into a production environment. A
security-conscious organization should be aware that the benefits of their
diligent testing process could be wiped out instantly by allowing the
security settings to be modified at runtime by changing a row or two in a
configuration database. If you have taken this into account (perhaps using
multiple layers of security within your application) then Spring Security
allows you to fully customize the source of security metadata. You can make
it fully dynamic if you choose. </para>
<para> Both method and web security are protected by subclasses of
<classname>AbstractSecurityInterceptor</classname> which is configured
with a <interfacename>SecurityMetadataSource</interfacename> from which it
obtains the metadata for a particular method or filter invocation <footnote>
<para>This class previouly went by the rather obscure name of
<classname>ObjectDefinitionSource</classname>, but has been
renamed in Spring Security 3.0</para>
</footnote>. For web security, the interceptor class is
<classname>FilterSecurityInterceptor</classname> and it uses the marker
interface
<interfacename>FilterInvocationSecurityMetadataSource</interfacename>.
The <quote>secured object</quote> type it operates on is a
<classname>FilterInvocation</classname>. The default implementation
which is used (both in the namespace <literal>&lt;http&gt;</literal> and
when configuring the interceptor explicitly, stores the list of URL patterns
and their corresponding list of <quote>configuration attributes</quote>
(instances of <interfacename>ConfigAttribute</interfacename>) in an
in-memory map. </para>
<para> To load the data from an alternative source, you must be using an
explicitly declared security filter chain (typically Spring Security's
<classname>FilterChainProxy</classname>) in order to customize the
<classname>FilterSecurityInterceptor</classname> bean. You can't use the
namespace. You would then implement
<interfacename>FilterInvocationSecurityMetadataSource</interfacename> to
load the data as you please for a particular
<classname>FilterInvocation</classname><footnote>
<para>The <classname>FilterInvocation</classname> object contains the
<classname>HttpServletRequest</classname>, so you can obtain the
URL or any other relevant information on which to base your decision
on what the list of returned attributes will contain.</para>
</footnote>. A very basic outline would look something like this: <programlisting language="java"><![CDATA[
public class MyFilterSecurityMetadataSource implements FilterInvocationSecurityMetadataSource {
public List<ConfigAttribute> getAttributes(Object object) {
FilterInvocation fi = (FilterInvocation) object;
String url = fi.getRequestUrl();
String httpMethod = fi.getRequest().getMethod();
List<ConfigAttribute> attributes = new ArrayList<ConfigAttribute>();
// Lookup your database (or other source) using this information and populate the
// list of attributes
return attributes;
}
public Collection<ConfigAttribute> getAllConfigAttributes() {
return null;
}
public boolean supports(Class<?> clazz) {
return FilterInvocation.class.isAssignableFrom(clazz);
}
}
]]></programlisting> For more information, look at the code for
<classname>DefaultFilterInvocationSecurityMetadataSource</classname>.
</para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-what-dependencies">
<question>
<para>How do I know which dependencies to add to my application to work with
Spring Security?</para>
</question>
<answer>
<para>It will depend on what features you are using and what type of application
you are developing. With Spring Security 3.0, the project jars are divided
into clearly distinct areas of functionality, so it is straightforward to
work out which Spring Security jars you need from your application
requirements. All applications will need the
<filename>spring-security-core</filename> jar. If you're developing a
web application, you need the <filename>spring-security-web</filename> jar.
If you're using security namespace configuration you need the
<filename>spring-security-config</filename> jar, for LDAP support you
need the <filename>spring-security-ldap</filename> jar and so on. </para>
<para> For third-party jars the situation isn't always quite so obvious. A good
starting point is to copy those from one of the pre-built sample
applications WEB-INF/lib directories. For a basic application, you can start
with the tutorial sample. If you want to use LDAP, with an embedded test
server, then use the LDAP sample as a starting point. </para>
<para> If you are building your project with maven, then adding the appropriate
Spring Security modules as dependencies to your pom.xml will automatically
pull in the core jars that the framework requires. Any which are marked as
"optional" in the Spring Security POM files will have to be added to your
own pom.xml file if you need them. </para>
</answer>
</qandaentry>
<qandaentry xml:id="faq-ldap-authorities">
<question>
<para>How do I authenticate against LDAP but load user roles from a
database?</para>
</question>
<answer>
<para> The <code>LdapAuthenticationProvider</code> bean (which handles normal
LDAP authentication in Spring Security) is configured with two separate
strategy interfaces, one which performs the authenticatation and one which
loads the user authorities, called
<interfacename>LdapAuthenticator</interfacename> and
<interfacename>LdapAuthoritiesPopulator</interfacename> respectively.
The <classname>DefaultLdapAuthoitiesPopulator</classname> loads the user
authorities from the LDAP directory and has various configuration parameters
to allow you to specify how these should be retrieved. </para>
<para> To use JDBC instead, you can implement the interface yourself, using
whatever SQL is appropriate for your schema: <programlisting language="java"><![CDATA[
public class MyAuthoritiesPopulator implements LdapAuthoritiesPopulator {
@Autowired
JdbcTemplate template;
List<GrantedAuthority> getGrantedAuthorities(DirContextOperations userData, String username) {
List<GrantedAuthority> = template.query("select role from roles where username = ?", new String[] {username}, new RowMapper<GrantedAuthority>() {
/**
* We're assuming here that you're using the standard convention of using the role
* prefix "ROLE_" to mark attributes which are supported by Spring Security's RoleVoter.
*/
public GrantedAuthority mapRow(ResultSet rs, int rowNum) throws SQLException {
return new GrantedAuthorityImpl("ROLE_" + rs.getString(1);
}
}
}
}
]]></programlisting> You would then add a bean of this type to your application context and inject
it into the <code>LdapAuthenticationProvider</code>. This is covered in the
section on configuring LDAP using explicit Spring beans in the LDAP chapter
of the reference manual. Note that you can't use the namespace for
configuration in this case. You should also consult the Javadoc for the
relevant classes and interfaces. </para>
</answer>
</qandaentry>
</qandadiv>
</qandaset>
</article>