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<html lang="en"><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><link href="./images/docs-stylesheet.css" rel="stylesheet" type="text/css"><title>Apache Tomcat 11 (11.0.5) - Realm Configuration How-To</title><meta name="author" content="Craig R. McClanahan"><meta name="author" content="Yoav Shapira"><meta name="author" content="Andrew R. Jaquith"></head><body><div id="wrapper"><header><div id="header"><div><div><div class="logo noPrint"><a href="https://tomcat.apache.org/"><img alt="Tomcat Home" src="./images/tomcat.png"></a></div><div style="height: 1px;"></div><div class="asfLogo noPrint"><a href="https://www.apache.org/" target="_blank"><img src="./images/asf-logo.svg" alt="The Apache Software Foundation" style="width: 266px; height: 83px;"></a></div><h1>Apache Tomcat 11</h1><div class="versionInfo">
            Version 11.0.5,
            <time datetime="2025-02-28">Feb 28 2025</time></div><div style="height: 1px;"></div><div style="clear: left;"></div></div></div></div></header><div id="middle"><div><div id="mainLeft" class="noprint"><div><nav><div><h2>Links</h2><ul><li><a href="index.html">Docs Home</a></li><li><a href="https://cwiki.apache.org/confluence/display/TOMCAT/FAQ">FAQ</a></li></ul></div><div><h2>User Guide</h2><ul><li><a href="introduction.html">1) Introduction</a></li><li><a href="setup.html">2) Setup</a></li><li><a href="appdev/index.html">3) First webapp</a></li><li><a href="deployer-howto.html">4) Deployer</a></li><li><a href="manager-howto.html">5) Manager</a></li><li><a href="host-manager-howto.html">6) Host Manager</a></li><li><a href="realm-howto.html">7) Realms and AAA</a></li><li><a href="jndi-resources-howto.html">8) JNDI Resources</a></li><li><a href="jndi-datasource-examples-howto.html">9) JDBC DataSources</a></li><li><a href="class-loader-howto.html">10) Classloading</a></li><li><a href="jasper-howto.html">11) JSPs</a></li><li><a href="ssl-howto.html">12) SSL/TLS</a></li><li><a href="ssi-howto.html">13) SSI</a></li><li><a href="cgi-howto.html">14) CGI</a></li><li><a href="proxy-howto.html">15) Proxy Support</a></li><li><a href="mbeans-descriptors-howto.html">16) MBeans Descriptors</a></li><li><a href="default-servlet.html">17) Default Servlet</a></li><li><a href="cluster-howto.html">18) Clustering</a></li><li><a href="balancer-howto.html">19) Load Balancer</a></li><li><a href="connectors.html">20) Connectors</a></li><li><a href="monitoring.html">21) Monitoring and Management</a></li><li><a href="logging.html">22) Logging</a></li><li><a href="apr.html">23) APR/Native</a></li><li><a href="virtual-hosting-howto.html">24) Virtual Hosting</a></li><li><a href="aio.html">25) Advanced IO</a></li><li><a href="maven-jars.html">26) Mavenized</a></li><li><a href="security-howto.html">27) Security Considerations</a></li><li><a href="windows-service-howto.html">28) Windows Service</a></li><li><a href="windows-auth-howto.html">29) Windows Authentication</a></li><li><a href="jdbc-pool.html">30) Tomcat's JDBC Pool</a></li><li><a href="web-socket-howto.html">31) WebSocket</a></li><li><a href="rewrite.html">32) Rewrite</a></li><li><a href="cdi.html">33) CDI 2 and JAX-RS</a></li><li><a href="graal.html">34) AOT/GraalVM Support</a></li></ul></div><div><h2>Reference</h2><ul><li><a href="RELEASE-NOTES.txt">Release Notes</a></li><li><a href="config/index.html">Configuration</a></li><li><a href="api/index.html">Tomcat Javadocs</a></li><li><a href="servletapi/index.html">Servlet 6.1 Javadocs</a></li><li><a href="jspapi/index.html">JSP 4.0 Javadocs</a></li><li><a href="elapi/index.html">EL 6.0 Javadocs</a></li><li><a href="websocketapi/index.html">WebSocket 2.2 Javadocs</a></li><li><a href="jaspicapi/index.html">Authentication 3.1 Javadocs</a></li><li><a href="annotationapi/index.html">Annotations 3.0 Javadocs</a></li><li><a href="https://tomcat.apache.org/connectors-doc/">JK 1.2 Documentation</a></li></ul></div><div><h2>Apache Tomcat Development</h2><ul><li><a href="building.html">Building</a></li><li><a href="changelog.html">Changelog</a></li><li><a href="https://cwiki.apache.org/confluence/display/TOMCAT/Tomcat+Versions">Status</a></li><li><a href="developers.html">Developers</a></li><li><a href="architecture/index.html">Architecture</a></li><li><a href="tribes/introduction.html">Tribes</a></li></ul></div></nav></div></div><div id="mainRight"><div id="content"><h2>Realm Configuration How-To</h2><h3 id="Table_of_Contents">Table of Contents</h3><div class="text">
<ul><li><a href="#Quick_Start">Quick Start</a></li><li><a href="#Overview">Overview</a><ol><li><a href="#What_is_a_Realm?">What is a Realm?</a></li><li><a href="#Configuring_a_Realm">Configuring a Realm</a></li></ol></li><li><a href="#Common_Features">Common Features</a><ol><li><a href="#Digested_Passwords">Digested Passwords</a></li><li><a href="#Example_Application">Example Application</a></li><li><a href="#Manager_Application">Manager Application</a></li><li><a href="#Realm_Logging">Realm Logging</a></li></ol></li><li><a href="#Standard_Realm_Implementations">Standard Realm Implementations</a><ol><li><a href="#DataSourceRealm">DataSourceRealm</a></li><li><a href="#JNDIRealm">JNDIRealm</a></li><li><a href="#UserDatabaseRealm">UserDatabaseRealm</a></li><li><a href="#MemoryRealm">MemoryRealm</a></li><li><a href="#JAASRealm">JAASRealm</a></li><li><a href="#CombinedRealm">CombinedRealm</a></li><li><a href="#LockOutRealm">LockOutRealm</a></li></ol></li></ul>
</div><h3 id="Quick_Start">Quick Start</h3><div class="text">

<p>This document describes how to configure Tomcat to support <em>container
managed security</em>, by connecting to an existing "database" of usernames,
passwords, and user roles.  You only need to care about this if you are using
a web application that includes one or more
<code>&lt;security-constraint&gt;</code> elements, and a
<code>&lt;login-config&gt;</code> element defining how users are required
to authenticate themselves.  If you are not utilizing these features, you can
safely skip this document.</p>

<p>For fundamental background information about container managed security,
see the <a href="https://cwiki.apache.org/confluence/display/TOMCAT/Specifications">Servlet
Specification (Version 2.4)</a>, Section 12.</p>

<p>For information about utilizing the <em>Single Sign On</em> feature of
Tomcat (allowing a user to authenticate themselves once across the entire
set of web applications associated with a virtual host), see
<a href="config/host.html#Single_Sign_On">here</a>.</p>

</div><h3 id="Overview">Overview</h3><div class="text">


<div class="subsection"><h4 id="What_is_a_Realm?">What is a Realm?</h4><div class="text">

<p>A <strong>Realm</strong> is a "database" of usernames and passwords that
identify valid users of a web application (or set of web applications), plus
an enumeration of the list of <em>roles</em> associated with each valid user.
You can think of roles as similar to <em>groups</em> in Unix-like operating
systems, because access to specific web application resources is granted to
all users possessing a particular role (rather than enumerating the list of
associated usernames).  A particular user can have any number of roles
associated with their username.</p>

<p>Although the Servlet Specification describes a portable mechanism for
applications to <em>declare</em> their security requirements (in the
<code>web.xml</code> deployment descriptor), there is no portable API
defining the interface between a servlet container and the associated user
and role information.  In many cases, however, it is desirable to "connect"
a servlet container to some existing authentication database or mechanism
that already exists in the production environment.  Therefore, Tomcat
defines a Java interface (<code>org.apache.catalina.Realm</code>) that
can be implemented by "plug in" components to establish this connection.
Six standard plug-ins are provided, supporting connections to various
sources of authentication information:</p>
<ul>
<li><a href="#DataSourceRealm">DataSourceRealm</a> - Accesses authentication
    information stored in a relational database, accessed via a named JNDI
    JDBC DataSource.</li>
<li><a href="#JNDIRealm">JNDIRealm</a> - Accesses authentication information
    stored in an LDAP based directory server, accessed via a JNDI provider.
    </li>
<li><a href="#UserDatabaseRealm">UserDatabaseRealm</a> - Accesses authentication
    information stored in an UserDatabase JNDI resource, which is typically
    backed by an XML document (<code>conf/tomcat-users.xml</code>).</li>
<li><a href="#MemoryRealm">MemoryRealm</a> - Accesses authentication
    information stored in an in-memory object collection, which is initialized
    from an XML document (<code>conf/tomcat-users.xml</code>).</li>
<li><a href="#JAASRealm">JAASRealm</a> - Accesses authentication information
    through the Java Authentication &amp; Authorization Service (JAAS)
    framework.</li>
</ul>

<p>It is also possible to write your own <code>Realm</code> implementation,
and integrate it with Tomcat.  To do so, you need to:</p>
<ul>
  <li>Implement <code>org.apache.catalina.Realm</code>,</li>
  <li>Place your compiled realm in $CATALINA_HOME/lib,</li>
  <li>Declare your realm as described in the "Configuring a Realm" section below,</li>
  <li>Declare your realm to the <a href="mbeans-descriptors-howto.html">MBeans Descriptors</a>.</li>
</ul>

</div></div>


<div class="subsection"><h4 id="Configuring_a_Realm">Configuring a Realm</h4><div class="text">

<p>Before getting into the details of the standard Realm implementations, it is
important to understand, in general terms, how a Realm is configured.  In
general, you will be adding an XML element to your <code>conf/server.xml</code>
configuration file, that looks something like this:</p>

<div class="codeBox"><pre><code>&lt;Realm className="... class name for this implementation"
       ... other attributes for this implementation .../&gt;</code></pre></div>

<p>The <code>&lt;Realm&gt;</code> element can be nested inside any one of
of the following <code>Container</code> elements.  The location of the
Realm element has a direct impact on the "scope" of that Realm
(i.e. which web applications will share the same authentication information):
</p>
<ul>
<li><em>Inside an &lt;Engine&gt; element</em> - This Realm will be shared
    across ALL web applications on ALL virtual hosts, UNLESS it is overridden
    by a Realm element nested inside a subordinate <code>&lt;Host&gt;</code>
    or <code>&lt;Context&gt;</code> element.</li>
<li><em>Inside a &lt;Host&gt; element</em> - This Realm will be shared across
    ALL web applications for THIS virtual host, UNLESS it is overridden
    by a Realm element nested inside a subordinate <code>&lt;Context&gt;</code>
    element.</li>
<li><em>Inside a &lt;Context&gt; element</em> - This Realm will be used ONLY
    for THIS web application.</li>
</ul>


</div></div>


</div><h3 id="Common_Features">Common Features</h3><div class="text">


<div class="subsection"><h4 id="Digested_Passwords">Digested Passwords</h4><div class="text">

<p>For each of the standard <code>Realm</code> implementations, the
user's password (by default) is stored in clear text.  In many
environments, this is undesirable because casual observers of the
authentication data can collect enough information to log on
successfully, and impersonate other users.  To avoid this problem, the
standard implementations support the concept of <em>digesting</em>
user passwords.  This allows the stored version of the passwords to be
encoded (in a form that is not easily reversible), but that the
<code>Realm</code> implementation can still utilize for
authentication.</p>

<p>When a standard realm authenticates by retrieving the stored
password and comparing it with the value presented by the user, you
can select digested passwords by placing a <a href="config/credentialhandler.html">
<code>CredentialHandler</code></a> element inside your <code>&lt;Realm&gt;</code>
element. An easy choice to support one of the algorithms SSHA, SHA or MD5
would be the usage of the <code>MessageDigestCredentialHandler</code>.
This element must be configured to one of the digest algorithms supported
by the <code>java.security.MessageDigest</code> class (SSHA, SHA or MD5).
When you select this option, the contents of the password that is stored
in the <code>Realm</code> must be the cleartext version of the password,
as digested by the specified algorithm.</p>

<p>When the <code>authenticate()</code> method of the Realm is called, the
(cleartext) password specified by the user is itself digested by the same
algorithm, and the result is compared with the value returned by the
<code>Realm</code>.  An equal match implies that the cleartext version of the
original password is the same as the one presented by the user, so that this
user should be authorized.</p>

<p>To calculate the digested value of a cleartext password, two convenience
techniques are supported:</p>
<ul>
<li>If you are writing an application that needs to calculate digested
    passwords dynamically, call the static <code>Digest()</code> method of the
    <code>org.apache.catalina.realm.RealmBase</code> class, passing the
    cleartext password, the digest algorithm name and the encoding as arguments.
    This method will return the digested password.</li>
<li>If you want to execute a command line utility to calculate the digested
    password, simply execute
<div class="codeBox"><pre><code>CATALINA_HOME/bin/digest.[bat|sh] -a {algorithm} {cleartext-password}</code></pre></div>
    and the digested version of this cleartext password will be returned to
    standard output.</li>
</ul>

<p>If using digested passwords with DIGEST authentication, the cleartext used
   to generate the digest is different and the digest must use one iteration of
   the MD5 algorithm with no salt. In the examples above
   <code>{cleartext-password}</code> must be replaced with
   <code>{username}:{realm}:{cleartext-password}</code>. For example, in a
   development environment this might take the form
   <code>testUser:Authentication required:testPassword</code>. The value for
   <code>{realm}</code> is taken from the <code>&lt;realm-name&gt;</code>
   element of the web application's <code>&lt;login-config&gt;</code>. If
   not specified in web.xml, the default value of <code>Authentication
   required</code> is used.</p>

<p>Usernames and/or passwords using encodings other than the platform default
are supported using</p>
<div class="codeBox"><pre><code>CATALINA_HOME/bin/digest.[bat|sh] -a {algorithm} -e {encoding} {input}</code></pre></div>
<p>but care is required to ensure that the input is correctly passed to the
digester. The digester returns <code>{input}:{digest}</code>. If the input
appears corrupted in the return, the digest will be invalid.</p>

<p>The output format of the digest is <code>{salt}${iterations}${digest}</code>.
If the salt length is zero and the iteration count is one, the output is
simplified to <code>{digest}</code>.</p>

<p>The full syntax of <code>CATALINA_HOME/bin/digest.[bat|sh]</code> is:</p>
<div class="codeBox"><pre><code>CATALINA_HOME/bin/digest.[bat|sh] [-a &lt;algorithm&gt;] [-e &lt;encoding&gt;]
        [-i &lt;iterations&gt;] [-s &lt;salt-length&gt;] [-k &lt;key-length&gt;]
        [-h &lt;handler-class-name&gt;] [-f &lt;password-file&gt; | &lt;credentials&gt;]
</code></pre></div>
<ul>
<li><b>-a</b> - The algorithm to use to generate the stored
                credential. If not specified, the default for the handler will
                be used. If neither handler nor algorithm is specified then a
                default of <code>SHA-512</code> will be used</li>
<li><b>-e</b> - The encoding to use for any byte to/from character
                conversion that may be necessary. If not specified, the
                system encoding (<code>Charset#defaultCharset()</code>) will
                be used.</li>
<li><b>-i</b> - The number of iterations to use when generating the
                stored credential. If not specified, the default for the
                CredentialHandler will be used.</li>
<li><b>-s</b> - The length (in bytes) of salt to generate and store as
                part of the credential. If not specified, the default for
                the CredentialHandler will be used.</li>
<li><b>-k</b> - The length (in bits) of the key(s), if any, created while
                generating the credential. If not specified, the default
                for the CredentialHandler will be used.</li>
<li><b>-h</b> - The fully qualified class name of the CredentialHandler
                to use. If not specified, the built-in handlers will be
                tested in turn (MessageDigestCredentialHandler then
                SecretKeyCredentialHandler) and the first one to accept the
                specified algorithm will be used.</li>
<li><b>-f</b> - The name of the file that contains passwords to encode. Each
                line in the file should contain only one password. Using this
                option ignores other password input.</li>
</ul>
</div></div>



<div class="subsection"><h4 id="Example_Application">Example Application</h4><div class="text">

<p>The example application shipped with Tomcat includes an area that is
protected by a security constraint, utilizing form-based login.  To access it,
point your browser at
<a href="http://localhost:8080/examples/jsp/security/protected/">http://localhost:8080/examples/jsp/security/protected/</a>
and log on with one of the usernames and passwords described for the default
<a href="#UserDatabaseRealm">UserDatabaseRealm</a>.</p>

</div></div>


<div class="subsection"><h4 id="Manager_Application">Manager Application</h4><div class="text">

<p>If you wish to use the <a href="manager-howto.html">Manager Application</a>
to deploy and undeploy applications in a running Tomcat installation, you
MUST add the "manager-gui" role to at least one username in your selected
Realm implementation.  This is because the manager web application itself uses a
security constraint that requires role "manager-gui" to access ANY request URI
within the HTML interface of that application.</p>

<p>For security reasons, no username in the default Realm (i.e. using
<code>conf/tomcat-users.xml</code> is assigned the "manager-gui" role.
Therefore, no one will be able to utilize the features of this application
until the Tomcat administrator specifically assigns this role to one or more
users.</p>

</div></div>

<div class="subsection"><h4 id="Realm_Logging">Realm Logging</h4><div class="text">

<p>Debugging and exception messages logged by a <code>Realm</code> will
   be recorded by the logging configuration associated with the container
   for the realm: its surrounding <a href="config/context.html">Context</a>,
   <a href="config/host.html">Host</a>, or
   <a href="config/engine.html">Engine</a>.</p>

</div></div>

</div><h3 id="Standard_Realm_Implementations">Standard Realm Implementations</h3><div class="text">

<div class="subsection"><h4 id="DataSourceRealm">DataSourceRealm</h4><div class="text">

<h5>Introduction</h5>

<p><strong>DataSourceRealm</strong> is an implementation of the Tomcat
<code>Realm</code> interface that looks up users in a relational database
accessed via a JNDI named JDBC DataSource.  There is substantial configuration
flexibility that lets you adapt to existing table and column names, as long
as your database structure conforms to the following requirements:</p>
<ul>
<li>There must be a table, referenced below as the <em>users</em> table,
    that contains one row for every valid user that this <code>Realm</code>
    should recognize.</li>
<li>The <em>users</em> table must contain at least two columns (it may
    contain more if your existing applications required it):
    <ul>
    <li>Username to be recognized by Tomcat when the user logs in.</li>
    <li>Password to be recognized by Tomcat when the user logs in.
        This value may in cleartext or digested - see below for more
        information.</li>
    </ul></li>
<li>There must be a table, referenced below as the <em>user roles</em> table,
    that contains one row for every valid role that is assigned to a
    particular user.  It is legal for a user to have zero, one, or more than
    one valid role.</li>
<li>The <em>user roles</em> table must contain at least two columns (it may
    contain more if your existing applications required it):
    <ul>
    <li>Username to be recognized by Tomcat (same value as is specified
        in the <em>users</em> table).</li>
    <li>Role name of a valid role associated with this user.</li>
    </ul></li>
</ul>

<h5>Quick Start</h5>

<p>To set up Tomcat to use DataSourceRealm, you will need to follow these steps:</p>
<ol>
<li>If you have not yet done so, create tables and columns in your database
    that conform to the requirements described above.</li>
<li>Configure a database username and password for use by Tomcat, that has
    at least read only access to the tables described above.  (Tomcat will
    never attempt to write to these tables.)</li>
<li>Configure a JNDI named JDBC DataSource for your database.  Refer to the
    <a href="jndi-datasource-examples-howto.html">JNDI DataSource Example
    How-To</a> for information on how to configure a JNDI named JDBC DataSource.
    Be sure to set the <code>Realm</code>'s <code>localDataSource</code>
    attribute appropriately, depending on where the JNDI DataSource is
    defined.</li>
<li>Set up a <code>&lt;Realm&gt;</code> element, as described below, in your
    <code>$CATALINA_BASE/conf/server.xml</code> file.</li>
<li>Restart Tomcat if it is already running.</li>
</ol>

<h5>Realm Element Attributes</h5>

<p>To configure DataSourceRealm, you will create a <code>&lt;Realm&gt;</code>
element and nest it in your <code>$CATALINA_BASE/conf/server.xml</code> file,
as described <a href="#Configuring_a_Realm">above</a>. The attributes for the
DataSourceRealm are defined in the <a href="config/realm.html">Realm</a>
configuration documentation.</p>

<h5>Example</h5>

<p>An example SQL script to create the needed tables might look something
like this (adapt the syntax as required for your particular database):</p>
<div class="codeBox"><pre><code>create table users (
  user_name         varchar(15) not null primary key,
  user_pass         varchar(15) not null
);

create table user_roles (
  user_name         varchar(15) not null,
  role_name         varchar(15) not null,
  primary key (user_name, role_name)
);</code></pre></div>

<p>Here is an example for using a MySQL database called "authority", configured
with the tables described above, and accessed with the JNDI JDBC DataSource with
name "java:/comp/env/jdbc/authority".</p>
<div class="codeBox"><pre><code>&lt;Realm className="org.apache.catalina.realm.DataSourceRealm"
   dataSourceName="jdbc/authority"
   userTable="users" userNameCol="user_name" userCredCol="user_pass"
   userRoleTable="user_roles" roleNameCol="role_name"/&gt;</code></pre></div>

<h5>Additional Notes</h5>

<p>DataSourceRealm operates according to the following rules:</p>
<ul>
<li>When a user attempts to access a protected resource for the first time,
    Tomcat will call the <code>authenticate()</code> method of this
    <code>Realm</code>.  Thus, any changes you have made to the database
    directly (new users, changed passwords or roles, etc.) will be immediately
    reflected.</li>
<li>Once a user has been authenticated, the user (and their associated
    roles) are cached within Tomcat for the duration of the user's login.
    (For FORM-based authentication, that means until the session times out or
    is invalidated; for BASIC authentication, that means until the user
    closes their browser).  The cached user is <strong>not</strong> saved and
    restored across sessions serialisations. Any changes to the database
    information for an already authenticated user will <strong>not</strong> be
    reflected until the next time that user logs on again.</li>
<li>Administering the information in the <em>users</em> and <em>user roles</em>
    table is the responsibility of your own applications.  Tomcat does not
    provide any built-in capabilities to maintain users and roles.</li>
</ul>

</div></div>


<div class="subsection"><h4 id="JNDIRealm">JNDIRealm</h4><div class="text">

<h5>Introduction</h5>

<p><strong>JNDIRealm</strong> is an implementation of the Tomcat
<code>Realm</code> interface that looks up users in an LDAP directory
server accessed by a JNDI provider (typically, the standard LDAP
provider that is available with the JNDI API classes). The realm
supports a variety of approaches to using a directory for
authentication.</p>

<h6>Connecting to the directory</h6>

<p>The realm's connection to the directory is defined by the
<strong>connectionURL</strong> configuration attribute. This is a URL
whose format is defined by the JNDI provider. It is usually an LDAP
URL that specifies the domain name of the directory server to connect
to, and optionally the port number and distinguished name (DN) of the
required root naming context.</p>

<p>If you have more than one provider you can configure an
<strong>alternateURL</strong>.  If a socket connection cannot be
made to the provider at the <strong>connectionURL</strong> an
attempt will be made to use the <strong>alternateURL</strong>.</p>

<p>When making a connection in order to search the directory and
retrieve user and role information, the realm authenticates itself to
the directory with the username and password specified by the
<strong>connectionName</strong> and
<strong>connectionPassword</strong> properties. If these properties
are not specified the connection is anonymous. This is sufficient in
many cases.
</p>


<h6>Selecting the user's directory entry</h6>

<p>Each user that can be authenticated must be represented in the
directory by an individual entry that corresponds to an element in the
initial <code>DirContext</code> defined by the
<strong>connectionURL</strong> attribute. This user entry must have an
attribute containing the username that is presented for
authentication.</p>

<p>Often the distinguished name of the user's entry contains the
username presented for authentication but is otherwise the same for
all users. In this case the <strong>userPattern</strong> attribute may
be used to specify the DN, with "{0}" marking where
the username should be substituted.</p>

<p>Otherwise the realm must search the directory to find a unique entry
containing the username. The following attributes configure this
search:</p>

     <ul>
     <li><strong>userBase</strong> - the entry that is the base of
         the subtree containing users.  If not specified, the search
         base is the top-level context.</li>

     <li><strong>userSubtree</strong> - the search scope. Set to
         <code>true</code> if you wish to search the entire subtree
         rooted at the <strong>userBase</strong> entry. The default value
         of <code>false</code> requests a single-level search
         including only the top level.</li>

     <li><strong>userSearch</strong> - pattern specifying the LDAP
         search filter to use after substitution of the username.</li>

    </ul>


<h6>Authenticating the user</h6>

<ul>
<li>
<p><b>Bind mode</b></p>

<p>By default the realm authenticates a user by binding to
the directory with the DN of the entry for that user and the password
presented by the user. If this simple bind succeeds the user is considered to
be authenticated.</p>

<p>For security reasons a directory may store a digest of the user's
password rather than the clear text version (see
<a href="#Digested_Passwords">Digested Passwords</a> for more information). In that case,
as part of the simple bind operation the directory automatically
computes the correct digest of the plaintext password presented by the
user before validating it against the stored value. In bind mode,
therefore, the realm is not involved in digest processing. The
<strong>digest</strong> attribute is not used, and will be ignored if
set.</p>
</li>

<li>
<p><b>Comparison mode</b></p>
<p>Alternatively, the realm may retrieve the stored
password from the directory and compare it explicitly with the value
presented by the user. This mode is configured by setting the
<strong>userPassword</strong> attribute to the name of a directory
attribute in the user's entry that contains the password.</p>

<p>Comparison mode has some disadvantages. First, the
<strong>connectionName</strong> and
<strong>connectionPassword</strong> attributes must be configured to
allow the realm to read users' passwords in the directory. For
security reasons this is generally undesirable; indeed many directory
implementations will not allow even the directory manager to read
these passwords. In addition, the realm must handle password digests
itself, including variations in the algorithms used and ways of
representing password hashes in the directory. However, the realm may
sometimes need access to the stored password, for example to support
HTTP Digest Access Authentication (RFC 2069). (Note that HTTP digest
authentication is different from the storage of password digests in
the repository for user information as discussed above).
</p>
</li>
</ul>

<h6>Assigning roles to the user</h6>

<p>The directory realm supports two approaches to the representation
of roles in the directory:</p>

<ul>
<li>
<p><b>Roles as explicit directory entries</b></p>

<p>Roles may be represented by explicit directory entries. A role
entry is usually an LDAP group entry with one attribute
containing the name of the role and another whose values are the
distinguished names or usernames of the users in that role.  The
following attributes configure a directory search to
find the names of roles associated with the authenticated user:</p>

<ul>
<li><strong>roleBase</strong> - the base entry for the role search.
    If not specified, the search base is the top-level directory
    context.</li>

<li><strong>roleSubtree</strong> - the search
    scope. Set to <code>true</code> if you wish to search the entire
    subtree rooted at the <code>roleBase</code> entry. The default
    value of <code>false</code> requests a single-level search
    including the top level only.</li>

<li><strong>roleSearch</strong> - the LDAP search filter for
    selecting role entries. It optionally includes pattern
    replacements "{0}" for the distinguished name and/or "{1}" for the
    username and/or "{2}" for an attribute from user's directory entry,
    of the authenticated user. Use <strong>userRoleAttribute</strong> to
    specify the name of the attribute that provides the value for "{2}".</li>

<li><strong>roleName</strong> - the attribute in a role entry
     containing the name of that role.</li>

<li><strong>roleNested</strong> - enable nested roles. Set to
     <code>true</code> if you want to nest roles in roles. If configured, then
     every newly found roleName and distinguished
     Name will be recursively tried for a new role search.
     The default value is <code>false</code>.</li>

</ul>

</li>
</ul>

<ul>
<li>
<p><b>Roles as an attribute of the user entry</b></p>

<p>Role names may also be held as the values of an attribute in the
user's directory entry. Use <strong>userRoleName</strong> to specify
the name of this attribute.</p>

</li>
</ul>
<p>A combination of both approaches to role representation may be used.</p>

<h5>Quick Start</h5>

<p>To set up Tomcat to use JNDIRealm, you will need to follow these steps:</p>
<ol>
<li>Make sure your directory server is configured with a schema that matches
    the requirements listed above.</li>
<li>If required, configure a username and password for use by Tomcat, that has
    read only access to the information described above.  (Tomcat will
    never attempt to modify this information.)</li>
<li>Set up a <code>&lt;Realm&gt;</code> element, as described below, in your
    <code>$CATALINA_BASE/conf/server.xml</code> file.</li>
<li>Restart Tomcat if it is already running.</li>
</ol>

<h5>Realm Element Attributes</h5>

<p>To configure JNDIRealm, you will create a <code>&lt;Realm&gt;</code>
element and nest it in your <code>$CATALINA_BASE/conf/server.xml</code> file,
as described <a href="#Configuring_a_Realm">above</a>. The attributes for the
JNDIRealm are defined in the <a href="config/realm.html">Realm</a> configuration
documentation.</p>

<h5>Example</h5>

<p>Creation of the appropriate schema in your directory server is beyond the
scope of this document, because it is unique to each directory server
implementation.  In the examples below, we will assume that you are using a
distribution of the OpenLDAP directory server (version 2.0.11 or later), which
can be downloaded from
<a href="https://www.openldap.org">https://www.openldap.org</a>.  Assume that
your <code>slapd.conf</code> file contains the following settings
(among others):</p>
<div class="codeBox"><pre><code>database ldbm
suffix dc="mycompany",dc="com"
rootdn "cn=Manager,dc=mycompany,dc=com"
rootpw secret</code></pre></div>

<p>We will assume for <code>connectionURL</code> that the directory
server runs on the same machine as Tomcat.  See <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/jndi/index.html">
http://docs.oracle.com/javase/7/docs/technotes/guides/jndi/index.html</a>
for more information about configuring and using the JNDI LDAP
provider.</p>

<p>Next, assume that this directory server has been populated with elements
as shown below (in LDIF format):</p>

<div class="codeBox"><pre><code># Define top-level entry
dn: dc=mycompany,dc=com
objectClass: dcObject
dc:mycompany

# Define an entry to contain people
# searches for users are based on this entry
dn: ou=people,dc=mycompany,dc=com
objectClass: organizationalUnit
ou: people

# Define a user entry for Janet Jones
dn: uid=jjones,ou=people,dc=mycompany,dc=com
objectClass: inetOrgPerson
uid: jjones
sn: jones
cn: janet jones
mail: j.jones@mycompany.com
userPassword: janet

# Define a user entry for Fred Bloggs
dn: uid=fbloggs,ou=people,dc=mycompany,dc=com
objectClass: inetOrgPerson
uid: fbloggs
sn: bloggs
cn: fred bloggs
mail: f.bloggs@mycompany.com
userPassword: fred

# Define an entry to contain LDAP groups
# searches for roles are based on this entry
dn: ou=groups,dc=mycompany,dc=com
objectClass: organizationalUnit
ou: groups

# Define an entry for the "tomcat" role
dn: cn=tomcat,ou=groups,dc=mycompany,dc=com
objectClass: groupOfUniqueNames
cn: tomcat
uniqueMember: uid=jjones,ou=people,dc=mycompany,dc=com
uniqueMember: uid=fbloggs,ou=people,dc=mycompany,dc=com

# Define an entry for the "role1" role
dn: cn=role1,ou=groups,dc=mycompany,dc=com
objectClass: groupOfUniqueNames
cn: role1
uniqueMember: uid=fbloggs,ou=people,dc=mycompany,dc=com</code></pre></div>

<p>An example <code>Realm</code> element for the OpenLDAP directory
server configured as described above might look like this, assuming
that users use their uid (e.g. jjones) to login to the
application and that an anonymous connection is sufficient to search
the directory and retrieve role information:</p>

<div class="codeBox"><pre><code>&lt;Realm   className="org.apache.catalina.realm.JNDIRealm"
     connectionURL="ldap://localhost:389"
       userPattern="uid={0},ou=people,dc=mycompany,dc=com"
          roleBase="ou=groups,dc=mycompany,dc=com"
          roleName="cn"
        roleSearch="(uniqueMember={0})"
/&gt;</code></pre></div>

<p>With this configuration, the realm will determine the user's
distinguished name by substituting the username into the
<code>userPattern</code>, authenticate by binding to the directory
with this DN and the password received from the user, and search the
directory to find the user's roles.</p>

<p>Now suppose that users are expected to enter their email address
rather than their userid when logging in. In this case the realm must
search the directory for the user's entry. (A search is also necessary
when user entries are held in multiple subtrees corresponding perhaps
to different organizational units or company locations).</p>

<p>Further, suppose that in addition to the group entries you want to
use an attribute of the user's entry to hold roles. Now the entry for
Janet Jones might read as follows:</p>

<div class="codeBox"><pre><code>dn: uid=jjones,ou=people,dc=mycompany,dc=com
objectClass: inetOrgPerson
uid: jjones
sn: jones
cn: janet jones
mail: j.jones@mycompany.com
memberOf: role2
memberOf: role3
userPassword: janet</code></pre></div>

<p> This realm configuration would satisfy the new requirements:</p>

<div class="codeBox"><pre><code>&lt;Realm   className="org.apache.catalina.realm.JNDIRealm"
     connectionURL="ldap://localhost:389"
          userBase="ou=people,dc=mycompany,dc=com"
        userSearch="(mail={0})"
      userRoleName="memberOf"
          roleBase="ou=groups,dc=mycompany,dc=com"
          roleName="cn"
        roleSearch="(uniqueMember={0})"
/&gt;</code></pre></div>

<p>Now when Janet Jones logs in as "j.jones@mycompany.com", the realm
searches the directory for a unique entry with that value as its mail
attribute and attempts to bind to the directory as
<code>uid=jjones,ou=people,dc=mycompany,dc=com</code> with the given
password. If authentication succeeds, they are assigned three roles:
"role2" and "role3", the values of the "memberOf" attribute in their
directory entry, and "tomcat", the value of the "cn" attribute in the
only group entry of which they are a member.</p>

<p>Finally, to authenticate the user by retrieving
the password from the directory and making a local comparison in the
realm, you might use a realm configuration like this:</p>

<div class="codeBox"><pre><code>&lt;Realm   className="org.apache.catalina.realm.JNDIRealm"
    connectionName="cn=Manager,dc=mycompany,dc=com"
connectionPassword="secret"
     connectionURL="ldap://localhost:389"
      userPassword="userPassword"
       userPattern="uid={0},ou=people,dc=mycompany,dc=com"
          roleBase="ou=groups,dc=mycompany,dc=com"
          roleName="cn"
        roleSearch="(uniqueMember={0})"
/&gt;</code></pre></div>

<p>However, as discussed above, the default bind mode for
authentication is usually to be preferred.</p>

<h5>Additional Notes</h5>

<p>JNDIRealm operates according to the following rules:</p>
<ul>
<li>When a user attempts to access a protected resource for the first time,
    Tomcat will call the <code>authenticate()</code> method of this
    <code>Realm</code>.  Thus, any changes you have made to the directory
    (new users, changed passwords or roles, etc.) will be immediately
    reflected.</li>
<li>Once a user has been authenticated, the user (and their associated
    roles) are cached within Tomcat for the duration of the user's login.
    (For FORM-based authentication, that means until the session times out or
    is invalidated; for BASIC authentication, that means until the user
    closes their browser).  The cached user is <strong>not</strong> saved and
    restored across sessions serialisations. Any changes to the directory
    information for an already authenticated user will <strong>not</strong> be
    reflected until the next time that user logs on again.</li>
<li>Administering the information in the directory server
    is the responsibility of your own applications.  Tomcat does not
    provide any built-in capabilities to maintain users and roles.</li>
</ul>

</div></div>


<div class="subsection"><h4 id="UserDatabaseRealm">UserDatabaseRealm</h4><div class="text">

<h5>Introduction</h5>

<p><strong>UserDatabaseRealm</strong> is an implementation of the Tomcat
<code>Realm</code> interface that uses a JNDI resource to store user
information. By default, the JNDI resource is backed by an XML file. It is not
designed for large-scale production use. At startup time, the UserDatabaseRealm
loads information about all users, and their corresponding roles, from an XML
document (by default, this document is loaded from
<code>$CATALINA_BASE/conf/tomcat-users.xml</code>). The users, their passwords
and their roles may all be editing dynamically, typically via JMX. Changes may
be saved and will be reflected in the XML file.</p>

<h5>Realm Element Attributes</h5>

<p>To configure UserDatabaseRealm, you will create a <code>&lt;Realm&gt;</code>
element and nest it in your <code>$CATALINA_BASE/conf/server.xml</code> file,
as described <a href="#Configuring_a_Realm">above</a>. The attributes for the
UserDatabaseRealm are defined in the <a href="config/realm.html">Realm</a>
configuration documentation.</p>

<h5>User File Format</h5>

<p>For the XML file based <code>UserDatabase</code>, the users file uses the
same format as the <a href="#MemoryRealm">MemoryRealm</a>.</p>

<h5>Example</h5>

<p>The default installation of Tomcat is configured with a UserDatabaseRealm
nested inside the <code>&lt;Engine&gt;</code> element, so that it applies
to all virtual hosts and web applications.  The default contents of the
<code>conf/tomcat-users.xml</code> file is:</p>
<div class="codeBox"><pre><code>&lt;tomcat-users&gt;
  &lt;user username="tomcat" password="tomcat" roles="tomcat" /&gt;
  &lt;user username="role1"  password="tomcat" roles="role1"  /&gt;
  &lt;user username="both"   password="tomcat" roles="tomcat,role1" /&gt;
&lt;/tomcat-users&gt;</code></pre></div>

<h5>Additional Notes</h5>

<p>UserDatabaseRealm operates according to the following rules:</p>
<ul>
<li>When Tomcat first starts up, it loads all defined users and their
    associated information from the users file. Changes made to the data in
    this file will <strong>not</strong> be recognized until Tomcat is
    restarted. Changes may be made via the UserDatabase resource. Tomcat
    provides MBeans that may be accessed via JMX for this purpose.</li>
<li>When a user attempts to access a protected resource for the first time,
    Tomcat will call the <code>authenticate()</code> method of this
    <code>Realm</code>.</li>
<li>Once a user has been authenticated, the user becomes associated within
    Tomcat for the duration of the user's login.
    (For FORM-based authentication, that means until the session times out or
    is invalidated; for BASIC authentication, that means until the user
    closes their browser). However, the user roles will still reflect the
    <code>UserDatabase</code> contents, unlike for the other realms. If a user
    is removed from the database, it will be considered to have no roles.
    The <code>useStaticPrincipal</code> attribute of the
    <code>UserDatabaseRealm</code> can be used to instead cache the user along
    with all its roles. The cached user is <strong>not</strong> saved and
    restored across sessions serialisations. When the user's principal object
    is serialized for any reason, it will also be replaced by a static
    equivalent object with roles that will no longer reflect the database
    contents.</li>
</ul>


</div></div>


<div class="subsection"><h4 id="MemoryRealm">MemoryRealm</h4><div class="text">

<h5>Introduction</h5>

<p><strong>MemoryRealm</strong> is a simple demonstration implementation of the
Tomcat <code>Realm</code> interface.  It is not designed for production use.
At startup time, MemoryRealm loads information about all users, and their
corresponding roles, from an XML document (by default, this document is loaded
from <code>$CATALINA_BASE/conf/tomcat-users.xml</code>).  Changes to the data
in this file are not recognized until Tomcat is restarted.</p>

<h5>Realm Element Attributes</h5>

<p>To configure MemoryRealm, you will create a <code>&lt;Realm&gt;</code>
element and nest it in your <code>$CATALINA_BASE/conf/server.xml</code> file,
as described <a href="#Configuring_a_Realm">above</a>. The attributes for the
MemoryRealm are defined in the <a href="config/realm.html">Realm</a>
configuration documentation.</p>

<h5>User File Format</h5>

<p>The users file (by default, <code>conf/tomcat-users.xml</code> must be an
XML document, with a root element <code>&lt;tomcat-users&gt;</code>.  Nested
inside the root element will be a <code>&lt;user&gt;</code> element for each
valid user, consisting of the following attributes:</p>
<ul>
<li><strong>name</strong> - Username this user must log on with.</li>
<li><strong>password</strong> - Password this user must log on with (in
    clear text if the <code>digest</code> attribute was not set on the
    <code>&lt;Realm&gt;</code> element, or digested appropriately as
    described <a href="#Digested_Passwords">here</a> otherwise).</li>
<li><strong>roles</strong> - Comma-delimited list of the role names
    associated with this user.</li>
</ul>

<h5>Additional Notes</h5>

<p>MemoryRealm operates according to the following rules:</p>
<ul>
<li>When Tomcat first starts up, it loads all defined users and their
    associated information from the users file.  Changes to the data in
    this file will <strong>not</strong> be recognized until Tomcat is
    restarted.</li>
<li>When a user attempts to access a protected resource for the first time,
    Tomcat will call the <code>authenticate()</code> method of this
    <code>Realm</code>.</li>
<li>Once a user has been authenticated, the user (and their associated
    roles) are cached within Tomcat for the duration of the user's login.
    (For FORM-based authentication, that means until the session times out or
    is invalidated; for BASIC authentication, that means until the user
    closes their browser).  The cached user is <strong>not</strong> saved and
    restored across sessions serialisations.</li>
<li>Administering the information in the users file is the responsibility
    of your application.  Tomcat does not
    provide any built-in capabilities to maintain users and roles.</li>
</ul>


</div></div>


<div class="subsection"><h4 id="JAASRealm">JAASRealm</h4><div class="text">

<h5>Introduction</h5>

        <p><strong>JAASRealm</strong> is an implementation of the Tomcat
<code>Realm</code> interface that authenticates users through the Java
Authentication &amp; Authorization Service (JAAS) framework which is now
provided as part of the standard Java SE API.</p>
        <p>Using JAASRealm gives the developer the ability to combine
practically any conceivable security realm with Tomcat's CMA. </p>
        <p>JAASRealm is prototype for Tomcat of the JAAS-based
J2EE authentication framework for J2EE v1.4, based on the <a href="https://www.jcp.org/en/jsr/detail?id=196">JCP Specification
Request 196</a> to enhance container-managed security and promote
'pluggable' authentication mechanisms whose implementations would be
container-independent.
        </p>
        <p>Based on the JAAS login module and principal (see <code>javax.security.auth.spi.LoginModule</code>
and <code>javax.security.Principal</code>), you can develop your own
security mechanism or wrap another third-party mechanism for
integration with the CMA as implemented by Tomcat.
        </p>

        <h5>Quick Start</h5>
        <p>To set up Tomcat to use JAASRealm with your own JAAS login module,
 you will need to follow these steps:</p>
        <ol>
          <li>Write your own LoginModule, User and Role classes based
on JAAS (see
<a href="http://docs.oracle.com/javase/7/docs/technotes/guides/security/jaas/tutorials/GeneralAcnOnly.html">
the JAAS Authentication Tutorial</a> and
<a href="http://docs.oracle.com/javase/7/docs/technotes/guides/security/jaas/JAASLMDevGuide.html">
the JAAS Login Module Developer's Guide</a>) to be managed by the JAAS Login
Context (<code>javax.security.auth.login.LoginContext</code>)
When developing your LoginModule, note that JAASRealm's built-in <code>CallbackHandler</code>
only recognizes the <code>NameCallback</code> and <code>PasswordCallback</code> at present.
          </li>
          <li>Although not specified in JAAS, you should create
separate classes to distinguish between users and roles, extending <code>javax.security.Principal</code>,
so that Tomcat can tell which Principals returned from your login
module are users and which are roles (see <code>org.apache.catalina.realm.JAASRealm</code>).
Regardless, the first Principal returned is <em>always</em> treated as the user Principal.
          </li>
          <li>Place the compiled classes on Tomcat's classpath
          </li>
          <li>Set up a login.config file for Java (see <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/security/jaas/tutorials/LoginConfigFile.html">
JAAS LoginConfig file</a>) and tell Tomcat where to find it by specifying
its location to the JVM, for instance by setting the environment
variable: <code>JAVA_OPTS=$JAVA_OPTS -Djava.security.auth.login.config==$CATALINA_BASE/conf/jaas.config</code></li>

          <li>Configure your security-constraints in your web.xml for
the resources you want to protect</li>
          <li>Configure the JAASRealm module in your server.xml </li>
          <li>Restart Tomcat if it is already running.</li>
        </ol>
        <h5>Realm Element Attributes</h5>
        <p>To configure JAASRealm as for step 6 above, you create
a <code>&lt;Realm&gt;</code> element and nest it in your
<code>$CATALINA_BASE/conf/server.xml</code>
file within your <code>&lt;Engine&gt;</code> node. The attributes for the
JAASRealm are defined in the <a href="config/realm.html">Realm</a>
configuration documentation.</p>

<h5>Example</h5>

<p>Here is an example of how your server.xml snippet should look.</p>

<div class="codeBox"><pre><code>&lt;Realm className="org.apache.catalina.realm.JAASRealm"
                appName="MyFooRealm"
    userClassNames="org.foobar.realm.FooUser"
     roleClassNames="org.foobar.realm.FooRole"/&gt;</code></pre></div>

<p>It is the responsibility of your login module to create and save User and
Role objects representing Principals for the user
(<code>javax.security.auth.Subject</code>). If your login module doesn't
create a user object but also doesn't throw a login exception, then the
Tomcat CMA will break and you will be left at the
http://localhost:8080/myapp/j_security_check URI or at some other
unspecified location.</p>

        <p>The flexibility of the JAAS approach is two-fold: </p>
        <ul>
          <li>you can carry out whatever processing you require behind
the scenes in your own login module.</li>
          <li>you can plug in a completely different LoginModule by changing the configuration
and restarting the server, without any code changes to your application.</li>
        </ul>

        <h5>Additional Notes</h5>
        <ul>
          <li>When a user attempts to access a protected resource for
              the first time, Tomcat will call the <code>authenticate()</code>
              method of this <code>Realm</code>.  Thus, any changes you have made in
              the security mechanism directly (new users, changed passwords or
              roles, etc.) will be immediately reflected.</li>
          <li>Once a user has been authenticated, the user (and their
              associated roles) are cached within Tomcat for the duration of
              the user's login.  For FORM-based authentication, that means until
              the session times out or is invalidated; for BASIC authentication,
              that means until the user closes their browser.  Any changes to the
              security information for an already authenticated user will <strong>not</strong>
              be reflected until the next time that user logs on again.</li>
          <li>As with other <code>Realm</code> implementations, digested passwords
              are supported if the <code>&lt;Realm&gt;</code> element in <code>server.xml</code>
              contains a <code>digest</code> attribute; JAASRealm's <code>CallbackHandler</code>
              will digest the password prior to passing it back to the <code>LoginModule</code></li>
        </ul>

</div></div>


<div class="subsection"><h4 id="CombinedRealm">CombinedRealm</h4><div class="text">

    <h5>Introduction</h5>

    <p><strong>CombinedRealm</strong> is an implementation of the Tomcat
    <code>Realm</code> interface that authenticates users through one or more
    sub-Realms.</p>

    <p>Using CombinedRealm gives the developer the ability to combine multiple
    Realms of the same or different types. This can be used to authenticate
    against different sources, provide fall back in case one Realm fails or for
    any other purpose that requires multiple Realms.</p>

    <p>Sub-realms are defined by nesting <code>Realm</code> elements inside the
    <code>Realm</code> element that defines the CombinedRealm. Authentication
    will be attempted against each <code>Realm</code> in the order they are
    listed. Authentication against any Realm will be sufficient to authenticate
    the user.</p>

    <h5>Realm Element Attributes</h5>
    <p>To configure a CombinedRealm, you create a <code>&lt;Realm&gt;</code>
    element and nest it in your <code>$CATALINA_BASE/conf/server.xml</code>
    file within your <code>&lt;Engine&gt;</code> or <code>&lt;Host&gt;</code>.
    You can also nest inside a <code>&lt;Context&gt;</code> node in a
    <code>context.xml</code> file.</p>

<h5>Example</h5>

<p>Here is an example of how your server.xml snippet should look to use a
UserDatabase Realm and a DataSource Realm.</p>

<div class="codeBox"><pre><code>&lt;Realm className="org.apache.catalina.realm.CombinedRealm" &gt;
   &lt;Realm className="org.apache.catalina.realm.UserDatabaseRealm"
             resourceName="UserDatabase"/&gt;
   &lt;Realm className="org.apache.catalina.realm.DataSourceRealm"
             dataSourceName="jdbc/authority"
             userTable="users" userNameCol="user_name" userCredCol="user_pass"
             userRoleTable="user_roles" roleNameCol="role_name"/&gt;
&lt;/Realm&gt;</code></pre></div>

</div></div>

<div class="subsection"><h4 id="LockOutRealm">LockOutRealm</h4><div class="text">

    <h5>Introduction</h5>

    <p><strong>LockOutRealm</strong> is an implementation of the Tomcat
    <code>Realm</code> interface that extends the CombinedRealm to provide lock
    out functionality to provide a user lock out mechanism if there are too many
    failed authentication attempts in a given period of time.</p>

    <p>To ensure correct operation, there is a reasonable degree of
    synchronisation in this Realm.</p>

    <p>This Realm does not require modification to the underlying Realms or the
    associated user storage mechanisms. It achieves this by recording all failed
    logins, including those for users that do not exist. To prevent a DOS by
    deliberating making requests with invalid users (and hence causing this
    cache to grow) the size of the list of users that have failed authentication
    is limited.</p>

    <p>Sub-realms are defined by nesting <code>Realm</code> elements inside the
    <code>Realm</code> element that defines the LockOutRealm. Authentication
    will be attempted against each <code>Realm</code> in the order they are
    listed. Authentication against any Realm will be sufficient to authenticate
    the user.</p>

    <h5>Realm Element Attributes</h5>
    <p>To configure a LockOutRealm, you create a <code>&lt;Realm&gt;</code>
    element and nest it in your <code>$CATALINA_BASE/conf/server.xml</code>
    file within your <code>&lt;Engine&gt;</code> or <code>&lt;Host&gt;</code>.
    You can also nest inside a <code>&lt;Context&gt;</code> node in a
    <code>context.xml</code> file. The attributes for the
    LockOutRealm are defined in the <a href="config/realm.html">Realm</a>
    configuration documentation.</p>

<h5>Example</h5>

<p>Here is an example of how your server.xml snippet should look to add lock out
functionality to a UserDatabase Realm.</p>

<div class="codeBox"><pre><code>&lt;Realm className="org.apache.catalina.realm.LockOutRealm" &gt;
   &lt;Realm className="org.apache.catalina.realm.UserDatabaseRealm"
             resourceName="UserDatabase"/&gt;
&lt;/Realm&gt;</code></pre></div>

</div></div>

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