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 5 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 5. However, doing this is beyond the scope of this document. See (FIXME - reference to developer stuff) for more information.

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:

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.

Introduction

JDBCRealm is an implementation of the Tomcat 5 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 5 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 5 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:

Example

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

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":

Additional Notes

JDBCRealm operates according to the following rules:

• When a user attempts to access a protected resource for the first time, Tomcat 5 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.

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:

Example

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

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".

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). 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.

Introduction

JNDIRealm is an implementation of the Tomcat 5 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.

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 userPattern attribute may be used to specify the DN, with "{0}" marking where the username should be substituted.

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 5 and by your apps).
4. Set up a <Realm> element, as described below, in your $CATALINA_HOME/conf/server.xml file.
5. Restart Tomcat 5 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:

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):

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):

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:

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.

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:

This realm configuration would satisfy the new requirements:

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:

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 5 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). 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.

Introduction

MemoryRealm is a simple demonstration implementation of the Tomcat 5 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:

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 5 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:

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 5 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.

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.

The example application shipped with Tomcat 5 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.

If you wish to use the Manager Application to deploy and undeploy applications in a running Tomcat 5 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.