Realm Configuration HOW-TO

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:

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:

If you have not yet done so, create tables and columns in your database that conform to the requirements described above.

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.)

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!

Set up a <Realm> element, as described below, in your $CATALINA_HOME/conf/server.xml file.

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&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). 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 a directory server accessed by a JNDI provider (typically, the standard LDAP provider that is available with the JNDI API classes). There is substantial configuration flexibility that lets you adapt to the existing schema inside your directory server, as long as it conforms to the following requirements:

Each user that can be authenticated is represented by an individual element in the top level DirContext that is accessed via the connectionURL attribute.

The user element must have the following characteristics:

The distinguished name (dn) attribute of this element contains the username that is presented for authentication.

There must be an attribute (identified by the userPassword attribute of our Realm element) that contains the user's password, either in clear text or digested (see below for more info).

Each group of users that has been assigned a particular role is represented by an individual element in the top level DirContext that is accessed via the connectionURL attribute.

The user group element must have the following characteristics:

The set of all possible groups of interest can be selected by an LDAP search pattern configured by the roleSearch attribute of our Realm element.

The roleSearch pattern optionally includes pattern replacements "{0}" for the distinguished name, and/or "{1} for the username, of the authenticated user for which roles will be retrieved.

The roleBase attribute can be set to the element that is the base of the search for matching roles. If not specified, the entire directory context will be searched.

The roleSubtree attribute can be set to true if you wish to search the entire subtree of the directory context. The default value of false requests a search of only the current level.

The element includes an attribute (whose name is configured by the roleName attribute of our Realm element) containing the name of the role represented by this element.

There must be an administrator username and password that Tomcat can use to establish a connection to the directory server, with at least read-only access to the information described above. A future version of Tomcat will support an option to use the user's username and password to attempt this connection.

Quick Start

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

Make sure your directory server is configured with a schema that matches the requirements listed above.

Configure a username and password for use by Tomcat, that has at least read only access to the information described above. (Tomcat will never attempt to modify this information.)

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).

Set up a <Realm> element, as described below, in your $CATALINA_HOME/conf/server.xml file.

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.JDBCRealm" here.

connectionName
The directory server username used to establish a JNDI connection.

connectionPassword
The directory server password used to establish a JNDI connection.

connectionURL
The directory server URL used to establish a JNDI connection.

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 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.

roleBase
The base element for role searches. If not specified, the top level element in the directory context will be used.

roleName
The name of the directory server attribute containing the role name.

roleSearch
An LDAP search pattern for selecting roles in this Realm, following the syntax supported by the java.text.MessageFormat class. Use {0} to substitute in the distinguished name of the user you want roles for, and/or {1} to substitute in the username of the user you want roles for.

roleSubtree
Set to true if you want role searches to search subtrees of the element selected by roleBase. The default value of false causes only the top level element to be searched.

userPassword
The name of the directory server attribute (in the user element) that contains the cleartext or digested user password (depending on the setting of the digest attribute).

userPattern
An LDAP search pattern for selecting users in this Realm, following the syntax supported by the java.text.MessageFormat class. Use {0} to substitute in the distinguished name of the user you want to select.

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
These settings help us identify values for the values to be specified for connectionName, and connectionPassword, and 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), which define the same users and roles as the default $CATALINA_HOME/conf/tomcat-users.xml does for MemoryRealm:
# Define a user named 'tomcat'
dn: cn=tomcat,dc=mycompany,dc=com
cn: tomcat
userPassword: tomcat
sn: Tomcat User
objectClass: person

# Define a user named 'role1'
dn: cn=role1,dc=mycompany,dc=com
cn: role1
userPassword: tomcat
sn: Role1 User
objectClass: person

# Define a user named 'both'
dn: cn=both,dc=mycompany,dc=com
cn: both
userPassword: tomcat
sn: Both User
objectClass: person

# Define an entry to base role searches on
dn: dc=roles,dc=mycompany,dc=com
cn: roles
objectClass: person
sn: Roles Entry

# Define all members of the 'tomcat' role
dn: cn=tomcat,dc=roles,dc=mycompany,dc=com
cn: tomcat
objectClass: groupOfUniqueNames
uniqueMember: cn=tomcat,dc=mycompany,dc=com
uniqueMember: cn=both,dc=mycompany,dc=com

# Define all members of the 'role1' role
dn: cn=role1,dc=roles,dc=mycompany,dc=com
cn: role1
objectClass: groupOfUniqueNames
uniqueMember: cn=role1,dc=mycompany,dc=com
uniqueMember: cn=both,dc=mycompany,dc=com
An example Realm element for the OpenLDAP directory server configured as described above might look like this:
<Realm   className="org.apache.catalina.realm.JNDIRealm" debug="99"
    connectionName="cn=Manager,dc=mycompany,dc=com"
connectionPassword="secret"
     connectionURL="ldap://localhost:389"
          roleBase="dc=roles,dc=mcclan,dc=net"
          roleName="cn"
        roleSearch="(uniqueMember={0})"
       roleSubtree="false"
      userPassword="userPassword"
       userPattern="cn={0},dc=mycompany,dc=com"
/>
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 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). 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 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).

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 causes 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.

Digested passwords are selected 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.