# The Tomcat 4 Servlet/JSP Container

## Realm Configuration HOW-TO

Table of Contents

> Quick Start

> > What is a Realm?
> > Configuring a Realm

> Standard Realm Implementations

> > JDBCRealm
> > DataSourceRealm
> > JNDIRealm
> > MemoryRealm

> Common Features

> > Digested Passwords
> > Example Application
> > Manager Application

Quick Start

> This document describes how to configure Tomcat to support container managed security, 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 `<security-constraint>` elements, and a `<login-config>` element defining how users are required to authenticate themselves. If you are not utilizing these features, you can safely skip this document.

> For fundamental background information about container managed security, see the Servlet Specification (Version 2.3), Section 12. For a more introductory level document for web application developers as well as administrators, see (FIXME - link to backgrounder on container managed security to be provided).

> For information about utilizing the Single Sign On feature of Tomcat 4 (allowing a user to authenticate themselves once across the entire set of web applications associated with a virtual host), see here.

Overview

> What is a Realm?

> > A Realm 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 roles associated with each valid user. You can think of roles as similar to groups 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.

> > Although the Servlet Specification describes a portable mechanism for applications to declare their security requirements (in the `web.xml` 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 desireable to "connect" a servlet container to some existing authentication database or mechanism that already exists in the production environment. Therefore, Tomcat 4 defines a Java interface (`org.apache.catalina.Realm`) that can be implemented by "plug in" components to establish this connection. Three standard plug-ins are provided, supporting connection to three different sources of authentication information:

> > - DataSourceRealm - Accesses authentication information stored in a relational database, accessed via a named JNDI JDBC DataSource.
> > - JDBCRealm - Accesses authentication information stored in a relational database, accessed via a JDBC driver.
> > - JNDIRealm - Accesses authentication information stored in an LDAP based directory server, accessed via a JNDI provider.
> > - MemoryRealm - Accesses authentication information stored in an in-memory object collection, which is initialized from an XML document (`conf/tomcat-users.xml`).

> > It is also possible to write your own `Realm` implementation, and integrate it with Tomcat 4. However, doing this is beyond the scope of this document. See (FIXME - reference to developer stuff) for more information.

> Configuring a Realm

> > 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 `conf/server.xml` configuration file, that looks something like this:

> >     <Realm className="... class name for this implementation"
> >            ... other attributes for this implementation .../>

> > The `<Realm>` element can be nested inside one of three different elements, which has a direct impact on the "scope" of that Realm (i.e. which web applications will share the same authentication information):

> > - Inside an <Engine> element - 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 `<Host>` or `<Context>` element.
> > - Inside a <Host> element - 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 `<Context>` element.
> > - Inside a <Context> element - This Realm will be used ONLY for THIS web application.

Standard Realm Implementations

> JDBCRealm

> > ### Introduction

> > JDBCRealm is an implementation of the Tomcat 4 `Realm` interface that looks up users in a relational database accessed via a JDBC driver. 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:

> > - There must be a table, referenced below as the users table, that contains one row for every valid user that this `Realm` should recognize.
> > - The users table must contain at least two columns (it may contain more if your existing applications required it):
> >   - Username to be recognized by Tomcat when the user logs in.
> >   - Password to be recognized by Tomcat when the user logs in. This value may in cleartext or digested - see below for more information.
> > - There must be a table, referenced below as the user roles 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.
> > - The user roles table must contain at least two columns (it may contain more if your existing applications required it):
> >   - Username to be recognized by Tomcat (same value as is specified in the users table).
> >   - Role name of a valid role associated with this user.

> > ### Quick Start

> > To set up Tomcat to use JDBCRealm, you will need to follow these steps:

> > 1. If you have not yet done so, create tables and columns in your database that conform to the requirements described above.
> > 2. 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.)
> > 3. Place a copy of the JDBC driver you will be using inside the `$CATALINA_HOME/server/lib` directory (if you do not need it visible to web applications) or `$CATALINA_HOME/common/lib` (if it will be used both by Tomcat 4 and by your apps). Note that only JAR files are recognized!
> > 4. Set up a `<Realm>` element, as described below, in your `$CATALINA_HOME/conf/server.xml` file.
> > 5. Restart Tomcat 4 if it is already running.

> > ### Realm Element Attributes

> > To configure JDBCRealm, you will create a `<Realm>` element and nest it in your `$CATALINA_HOME/conf/server.xml` file, as described above. The following attributes are supported by this implementation:

> > Attribute | Description
> > --- | ---
> > `className` | The fully qualified Java class name of this Realm implementation. You MUST specify the value "`org.apache.catalina.realm.JDBCRealm`" here.
> > `connectionName` | The database username used to establish a JDBC connection.
> > `connectionPassword` | The database password used to establish a JDBC connection.
> > `connectionURL` | The database URL used to establish a JDBC connection.
> > `debug` | The level of debugging detail logged by this Realm to the associated Logger. Higher numbers generate more detailed output. If not specified, the default debugging detail level is zero (0).
> > `digest` | The digest algorithm used to store passwords in non-plaintext formats. Valid values are those accepted for the algorithm name by the `java.security.MessageDigest` class. See Digested Passwords for more information. If not specified, passwords are stored in clear text.
> > `driverName` | The fully qualified Java class name of the JDBC driver to be used. Consult the documentation for your JDBC driver for the appropriate value.
> > `roleNameCol` | The name of the column, in the user roles table, that contains the name of a role assigned to this user.
> > `userCredCol` | The name of the column, in the users table, that contains the password for this user (either in clear text, or digested if the `digest` attribute is set).
> > `userNameCol` | The name of the column, in the users and user roles tables, that contains the username of this user.
> > `userRoleTable` | The name of the table that contains one row for each role assigned to a particular username. This table must include at least the columns named by the `userNameCol` and `roleNameCol` attributes.
> > `userTable` | The name of the table that contains one row for each username to be recognized by Tomcat. This table must include at least the columns named by the `userNameCol` and `userCredCol` attributes.

> > ### Example

> > An example SQL script to create the needed tables might look something like this (adapt the syntax as required for your particular database):

> >     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)
> >     );

> > Example `Realm` elements are included (commented out) in the default `$CATALINA_HOME/conf/server.xml` file. Here's an example for using a MySQL database called "authority", configured with the tables described above, and accessed with username "dbuser" and password "dbpass":

> >     <Realm className="org.apache.catalina.realm.JDBCRealm" debug="99"
> >           driverName="org.gjt.mm.mysql.Driver"
> >        connectionURL="jdbc:mysql://localhost/authority?user=dbuser&amp;password=dbpass"
> >            userTable="users" userNameCol="user_name" userCredCol="user_pass"
> >        userRoleTable="user_roles" roleNameCol="role_name"/>

> > ### Additional Notes

> > JDBCRealm operates according to the following rules:

> > - When a user attempts to access a protected resource for the first time, Tomcat 4 will call the `authenticate()` method of this `Realm`. Thus, any changes you have made to the database directly (new users, changed passwords or roles, etc.) will be immediately reflected.
> > - Once a user has been authenticated, the user (and his or her 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 not saved and restored across sessions serialisations. Any changes to the database information for an already authenticated user will not be reflected until the next time that user logs on again.
> > - Administering the information in the users and user roles table is the responsibility of your own applications. Tomcat does not provide any built-in capabilities to maintain users and roles.
> > - Debugging and exception messages logged by this `Realm` will be recorded by the `Logger` that is associated with our surrounding `Context`, `Host`, or `Engine`. By default, the corresponding Logger will create a log file in the `$CATALINA_HOME/logs` directory.

> DataSourceRealm

> > ### Introduction

> > DataSourceRealm is an implementation of the Tomcat 4 `Realm` 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:

> > - There must be a table, referenced below as the users table, that contains one row for every valid user that this `Realm` should recognize.
> > - The users table must contain at least two columns (it may contain more if your existing applications required it):
> >   - Username to be recognized by Tomcat when the user logs in.
> >   - Password to be recognized by Tomcat when the user logs in. This value may in cleartext or digested - see below for more information.
> > - There must be a table, referenced below as the user roles 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.
> > - The user roles table must contain at least two columns (it may contain more if your existing applications required it):
> >   - Username to be recognized by Tomcat (same value as is specified in the users table).
> >   - Role name of a valid role associated with this user.

> > ### Quick Start

> > To set up Tomcat to use DataSourceRealm, you will need to follow these steps:

> > 1. If you have not yet done so, create tables and columns in your database that conform to the requirements described above.
> > 2. 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.)
> > 3. Configure a JNDI named JDBC DataSource for your database. Refer to the JNDI DataSource Example HOW-TO for information on how to configure a JNDI named JDBC DataSource.
> > 4. Set up a `<Realm>` element, as described below, in your `$CATALINA_HOME/conf/server.xml` file.
> > 5. Restart Tomcat 4 if it is already running.

> > ### Realm Element Attributes

> > To configure DataSourceRealm, you will create a `<Realm>` element and nest it in your `$CATALINA_HOME/conf/server.xml` file, as described above. The following attributes are supported by this implementation:

> > Attribute | Description
> > --- | ---
> > `className` | The fully qualified Java class name of this Realm implementation. You MUST specify the value "`org.apache.catalina.realm.DataSourceRealm`" here.
> > `dataSourceName` | The JNDI named JDBC DataSource for your database.
> > `debug` | The level of debugging detail logged by this Realm to the associated Logger. Higher numbers generate more detailed output. If not specified, the default debugging detail level is zero (0).
> > `digest` | The digest algorithm used to store passwords in non-plaintext formats. Valid values are those accepted for the algorithm name by the `java.security.MessageDigest` class. See Digested Passwords for more information. If not specified, passwords are stored in clear text.
> > `roleNameCol` | The name of the column, in the user roles table, that contains the name of a role assigned to this user.
> > `userCredCol` | The name of the column, in the users table, that contains the password for this user (either in clear text, or digested if the `digest` attribute is set).
> > `userNameCol` | The name of the column, in the users and user roles tables, that contains the username of this user.
> > `userRoleTable` | The name of the table that contains one row for each role assigned to a particular username. This table must include at least the columns named by the `userNameCol` and `roleNameCol` attributes.
> > `userTable` | The name of the table that contains one row for each username to be recognized by Tomcat. This table must include at least the columns named by the `userNameCol` and `userCredCol` attributes.

> > ### Example

> > An example SQL script to create the needed tables might look something like this (adapt the syntax as required for your particular database):

> >     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)
> >     );

> > 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".

> >     <Realm className="org.apache.catalina.realm.DataSourceRealm" debug="99"
> >        dataSourceName="java:/comp/env/jdbc/authority"
> >        userTable="users" userNameCol="user_name" userCredCol="user_pass"
> >        userRoleTable="user_roles" roleNameCol="role_name"/>

> > ### Additional Notes

> > DataSourceRealm operates according to the following rules:

> > - When a user attempts to access a protected resource for the first time, Tomcat 4 will call the `authenticate()` method of this `Realm`. Thus, any changes you have made to the database directly (new users, changed passwords or roles, etc.) will be immediately reflected.
> > - Once a user has been authenticated, the user (and his or her 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 not saved and restored across sessions serialisations. Any changes to the database information for an already authenticated user will not be reflected until the next time that user logs on again.
> > - Administering the information in the users and user roles table is the responsibility of your own applications. Tomcat does not provide any built-in capabilities to maintain users and roles.
> > - Debugging and exception messages logged by this `Realm` will be recorded by the `Logger` that is associated with our surrounding `Context`, `Host`, or `Engine`. By default, the corresponding Logger will create a log file in the `$CATALINA_HOME/logs` directory.

> JNDIRealm

> > ### Introduction

> > JNDIRealm is an implementation of the Tomcat 4 `Realm` 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.

> > #### Connecting to the directory

> > The realm's connection to the directory is defined by the connectionURL 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.

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

> > 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 connectionName and connectionPassword properties. If these properties are not specified the connection is anonymous. This is sufficient in many cases.

> > #### Selecting the user's directory entry

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

> > There are multiple options for specifying where to look for users. One is through the use of userPattern. This is set to the distinguished name of the user entry, but with "{0}" marking where the username should be substituted. If you want Tomcat to search for the username in multiple places, you can supply multiple locations in the userPattern. This is done by surrounding each separate location with parentheses. For example, "(cn={0},ou=users1,o=myorg)(cn={0},ou=users2,o=myorg)" will result in Tomcat looking in ou=users1,o=myorg, and then ou=users2,o=myorg for the username passed in from the authentication process. You can also use the standard LDAP "OR" search format, for instance "(|(cn={0},o=myorg)({0}))". Note that, as in this example, you can do both context-less and fully-typed logins using this technique.

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

> > - userBase - the entry that is the base of the subtree containing users. If not specified, the search base is the top-level context.
> > - userSubtree - the search scope. Set to `true` if you wish to search the entire subtree rooted at the userBase entry. The default value of `false` requests a single-level search including only the top level.
> > - userSearch - pattern specifying the LDAP search filter to use after substitution of the username.

> > #### Authenticating the user

> > - Bind mode

> >   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.

> >   For security reasons a directory may store a digest of the user's password rather than the clear text version (see Digested Passwords 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 digest attribute is not used, and will be ignored if set.

> > - Comparison mode

> >   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 userPassword attribute to the name of a directory attribute in the user's entry that contains the password.

> >   Comparison mode has some disadvantages. First, the connectionName and connectionPassword 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).

> > #### Assigning roles to the user

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

> > - Roles as explicit directory entries

> >   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:

> >   - roleBase - the base entry for the role search. If not specified, the search base is the top-level directory context.
> >   - roleSubtree - the search scope. Set to `true` if you wish to search the entire subtree rooted at the `roleBase` entry. The default value of `false` requests a single-level search including the top level only.
> >   - roleSearch - the LDAP search filter for selecting role entries. It optionally includes pattern replacements "{0}" for the distinguished name and/or "{1}" for the username of the authenticated user.
> >   - roleName - the attribute in a role entry containing the name of that role.

> > - Roles as an attribute of the user entry

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

> > A combination of both approaches to role representation may be used.

> > ### Quick Start

> > To set up Tomcat to use JNDIRealm, you will need to follow these steps:

> > 1. Make sure your directory server is configured with a schema that matches the requirements listed above.
> > 2. 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.)
> > 3. Place a copy of the JNDI driver you will be using (typically `ldap.jar` available with JNDI) inside the `$CATALINA_HOME/server/lib` directory (if you do not need it visible to web applications) or `$CATALINA_HOME/common/lib` (if it will be used both by Tomcat 4 and by your apps).
> > 4. Set up a `<Realm>` element, as described below, in your `$CATALINA_HOME/conf/server.xml` file.
> > 5. Restart Tomcat 4 if it is already running.

> > ### Realm Element Attributes

> > To configure JNDIRealm, you will create a `<Realm>` element and nest it in your `$CATALINA_HOME/conf/server.xml` file, as described above. The following attributes are supported by this implementation:

> > Attribute | Description
> > --- | ---
> > `className` | The fully qualified Java class name of this Realm implementation. You MUST specify the value "`org.apache.catalina.realm.JNDIRealm`" here.
> > `connectionName` | The directory username to use when establishing a connection to the directory for LDAP search operations. If not specified an anonymous connection is made, which is often sufficient unless you specify the `userPassword` property.
> > `connectionPassword` | The directory password to use when establishing a connection to the directory for LDAP search operations. If not specified an anonymous connection is made, which is often sufficient unless you specify the `userPassword` property.
> > `connectionURL` | The connection URL to be passed to the JNDI driver when establishing a connection to the directory.
> > `contextFactory` | The fully qualified Java class name of the JNDI context factory to be used for this connection. By default, the standard JNDI LDAP provider is used (`com.sun.jndi.ldap.LdapCtxFactory`).
> > `debug` | The level of debugging detail logged by this Realm to the associated Logger. Higher numbers generate more detailed output. If not specified, the default debugging detail level is zero (0).

> > `digest`

> > The digest algorithm to apply to the plaintext password offered by the user before comparing it with the value retrieved from the directory. Valid values are those accepted for the algorithm name by the `java.security.MessageDigest` class. See Digested Passwords for more information. If not specified the plaintext password is assumed to be retrieved. Not required unless `userPassword` is specified

> > `roleBase` | The base directory entry for performing role searches. If not specified, the top level element in the directory context will be used.
> > `roleName` | The name of the attribute that contains role names in the directory entries found by a role search. In addition you can use the `userRoleName` property to specify the name of an attribute, in the user's entry, containing additional role names. If `roleName` is not specified a role search does not take place, and roles are taken only from the user's entry.

> > `roleSearch`

> > The LDAP filter expression used for performing role searches, following the syntax supported by the `java.text.MessageFormat` class. Use `{0}` to substitute the distinguished name (DN) of the user, and/or `{1}` to substitute the username. If not specified a role search does not take place and roles are taken only from the attribute in the user's entry specified by the `userRoleName` property.

> > `roleSubtree` | Set to `true` if you want to search the entire subtree of the element specified by the `roleBase` property for role entries associated with the user. The default value of `false` causes only the top level to be searched.
> > `userBase` | The base element for user searches performed using the `userSearch` expression. If not specified, the top level element in the directory context will be used. Not used if you are using the `userPattern` expression.

> > `userPassword`

> > Name of the attribute in the user's entry containing the user's password. If you specify this value, JNDIRealm will bind to the directory using the values specified by `connectionName` and `connectionPassword` properties, and retrieve the corresponding attribute for comparison to the value specified by the user being authenticated. If the `digest` attribute is set, the specified digest algorithm is applied to the password offered by the user before comparing it with the value retrieved from the directory. If you do not specify this value, JNDIRealm will attempt a simple bind to the directory using the DN of the user's entry and password specified by the user, with a successful bind being interpreted as an authenticated user.

> > `userPattern`

> > A pattern for the distinguished name (DN) of the user's directory entry, following the syntax supported by the `java.text.MessageFormat` class with `{0}` marking where the actual username should be inserted. Multiple search locations are achieved by separating each with parentheses. You can use this property instead of `userSearch`, `userSubtree` and `userBase` when the distinguished name contains the username and is otherwise the same for all users.

> > `userRoleName` | The name of an attribute in the user's directory entry containing zero or more values for the names of roles assigned to this user. In addition you can use the `roleName` property to specify the name of an attribute to be retrieved from individual role entries found by searching the directory. If `userRoleName` is not specified all the roles for a user derive from the role search.
> > `userSearch` | The LDAP filter expression to use when searching for a user's directory entry, with `{0}` marking where the actual username should be inserted. Use this property (along with the `userBase` and `userSubtree` properties) instead of `userPattern` to search the directory for the user's entry.
> > `userSubtree` | Set to `true` if you want to search the entire subtree of the element specified by the `userBase` property for the user's entry. The default value of `false` causes only the top level to be searched. Not used if you are using the `userPattern` expression.

> > ### Example

> > 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 http://www.openldap.org. Assume that your `slapd.conf` file contains the following settings (among others):

> >     database ldbm
> >     suffix dc="mycompany",dc="com"
> >     rootdn "cn=Manager,dc=mycompany,dc=com"
> >     rootpw secret

> > We will assume for `connectionURL` that the directory server runs on the same machine as Tomcat. See http://java.sun.com/products/jndi/docs.html for more information about configuring and using the JNDI LDAP provider.

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

> >     # 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 another entry to contain admin users
> >     # searches for admin users are based on this entry
> >     dn: ou=admins,dc=mycompany,dc=com
> >     objectClass: organizationalUnit
> >     ou: admins

> >     # 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 a user entry for an admin user
> >     dn: uid=jsmith,ou=admins,dc=mycompany,dc=com
> >     objectClass: inetOrgPerson
> >     uid: jsmith
> >     sn: smith
> >     cn: jean smith
> >     mail: j.smith@mycompany.com
> >     userPassword: jean

> >     # 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
> >     uniqueMember: uid=jsmith,ou=admins,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

> > An example `Realm` 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:

> >     <Realm   className="org.apache.catalina.realm.JNDIRealm" debug="99"
> >          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})"
> >     />

> > With this configuration, the realm will determine the user's distinguished name by substituting the username into the `userPattern`, 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.

> > If you want the realm to look in multiple pre-determined locations, you can use a similar notation, surrounding each location by parentheses:

> >     <Realm   className="org.apache.catalina.realm.JNDIRealm" debug="99"
> >          connectionURL="ldap://localhost:389"
> >            userPattern="(uid={0},ou=people,dc=mycompany,dc=com)(uid={0},ou=admins,dc=mycompany,dc=com)"
> >               roleBase="ou=groups,dc=mycompany,dc=com"
> >               roleName="cn"
> >             roleSearch="(uniqueMember={0})"
> >     />

> > This pre-supposes that the User IDs in these two groups are unique; the first `userPattern` that results in a valid user ID will be the one used. Note that you can support typeless logins as well by adding "({0})" to the userPattern string above. Then, Jean Smith can log in as "jsmith", or "uid=jsmith,ou=admins,dc=mycompany,dc=com".

> > 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).

> > 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:

> >     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

> > This realm configuration would satisfy the new requirements:

> >     <Realm   className="org.apache.catalina.realm.JNDIRealm" debug="99"
> >          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})"
> >     />

> > 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 `uid=jjones,ou=people,dc=mycompany,dc=com` with the given password. If authentication succeeds, she is assigned three roles: "role2" and "role3", the values of the "memberOf" attribute in her directory entry, and "tomcat", the value of the "cn" attribute in the only group entry of which she is a member.

> > 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:

> >     <Realm   className="org.apache.catalina.realm.JNDIRealm" debug="99"
> >         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})"
> >     />

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

> > ### Additional Notes

> > JNDIRealm operates according to the following rules:

> > - When a user attempts to access a protected resource for the first time, Tomcat 4 will call the `authenticate()` method of this `Realm`. Thus, any changes you have made to the directory (new users, changed passwords or roles, etc.) will be immediately reflected.
> > - Once a user has been authenticated, the user (and his or her 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 not saved and restored across sessions serialisations. Any changes to the directory information for an already authenticated user will not be reflected until the next time that user logs on again.
> > - 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.
> > - Debugging and exception messages logged by this `Realm` will be recorded by the `Logger` that is associated with our surrounding `Context`, `Host`, or `Engine`. By default, the corresponding Logger will create a log file in the `$CATALINA_HOME/logs` directory.

> MemoryRealm

> > ### Introduction

> > MemoryRealm is a simple demonstration implementation of the Tomcat 4 `Realm` 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 `$CATALINA_HOME/conf/tomcat-users.xml`). Changes to the data in this file are not recognized until Tomcat is restarted.

> > ### Realm Element Attributes

> > To configure MemoryRealm, you will create a `<Realm>` element and nest it in your `$CATALINA_HOME/conf/server.xml` file, as described above. The following attributes are supported by this implementation:

> > Attribute | Description
> > --- | ---
> > `className` | The fully qualified Java class name of this Realm implementation. You MUST specify the value "`org.apache.catalina.realm.MemoryRealm`" here.
> > `debug` | The level of debugging detail logged by this Realm to the associated Logger. Higher numbers generate more detailed output. If not specified, the default debugging detail level is zero (0).
> > `digest` | The digest algorithm used to store passwords in non-plaintext formats. Valid values are those accepted for the algorithm name by the `java.security.MessageDigest` class. See Digested Passwords for more information. If not specified, passwords are stored in clear text.
> > `pathname` | Absolute or relative (to $CATALINA_HOME) pathname of the XML document containing our valid usernames, passwords, and roles. See below for more information on the format of this file. If not specified, the value `conf/tomcat-users.xml` is used.

> > ### User File Format

> > The users file (by default, `conf/tomcat-users.xml` must be an XML document, with a root element `<tomcat-users>`. Nested inside the root element will be a `<user>` element for each valid user, consisting of the following attributes:

> > - name - Username this user must log on with.
> > - password - Password this user must log on with (in clear text if the `digest` attribute was not set on the `<Realm>` element, or digested appropriately as described here otherwise).
> > - roles - Comma-delimited list of the role names associated with this user.

> > ### Example

> > The default installation of Tomcat 4 is configured with a MemoryRealm nested inside the `<Engine>` element, so that it applies to all virtual hosts and web applications. The default contents of the `conf/tomcat-users.xml` file is:

> >     <tomcat-users>
> >       <user name="tomcat" password="tomcat" roles="tomcat" />
> >       <user name="role1"  password="tomcat" roles="role1"  />
> >       <user name="both"   password="tomcat" roles="tomcat,role1" />
> >     </tomcat-users>

> > ### Additional Notes

> > MemoryRealm operates according to the following rules:

> > - 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 not be recognized until Tomcat is restarted.
> > - When a user attempts to access a protected resource for the first time, Tomcat 4 will call the `authenticate()` method of this `Realm`.
> > - Once a user has been authenticated, the user (and his or her 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 not saved and restored across sessions serialisations.
> > - 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.
> > - Debugging and exception messages logged by this `Realm` will be recorded by the `Logger` that is associated with our surrounding `Context`, `Host`, or `Engine`. By default, the corresponding Logger will create a log file in the `$CATALINA_HOME/logs` directory.

Common Features

> Digested Passwords

> > For each of the standard `Realm` implementations, the user's password (by default) is stored in clear text. In many environments, this is undesireable 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 digesting user passwords. This allows the stored version of the passwords to be encoded (in a form that is not easily reversible), but that the `Realm` implementation can still utilize for authentication.

> > 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 specifying the `digest` attribute on your `<Realm>` element. The value for this attribute must be one of the digest algorithms supported by the `java.security.MessageDigest` class (SHA, MD2, or MD5). When you select this option, the contents of the password that is stored in the `Realm` must be the cleartext version of the password, as digested by the specified algorithm.

> > When the `authenticate()` 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 `Realm`. 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.

> > To calculate the digested value of a cleartext password, two convenience techniques are supported:

> > - If you are writing an application that needs to calculate digested passowrds dynamically, call the static `Digest()` method of the `org.apache.catalina.realm.RealmBase` class, passing the cleartext password and the digest algorithm name as arguments. This method will return the digested password.
> > - If you want to execute a command line utility to calculate the digested password, simply execute

> >       java org.apache.catalina.realm.RealmBase \
> >           -a {algorithm} {cleartext-password}

> >   and the digested version of this cleartext password will be returned to standard output.

> > To use either of the above techniques, the `$CATALINA_HOME/server/lib/catalina.jar` file will need to be on your class path to make the `RealmBase` class available.

> Example Application

> > The example application shipped with Tomcat 4 includes an area that is protected by a security constraint, utilizing form-based login. To access it, point your browser at http://localhost:8080/examples/jsp/security/protected/ and log on with one of the usernames and passwords described for the default MemoryRealm.

> Manager Application

> > If you wish to use the Manager Application to deploy and undeploy applications in a running Tomcat 4 installation, you MUST add the "manager" 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" to access ANY request URI within that application.

> > For security reasons, no username in the default Realm (i.e. using `conf/tomcat-users.xml` is assigned the "manager" role. Therfore, 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.

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