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 6 defines a Java interface (org.apache.catalina.Realm) that can be implemented by "plug in" components to establish this connection. Five standard plug-ins are provided, supporting connections to various sources of authentication information:

• JDBCRealm?- Accesses authentication information stored in a relational database, accessed via a JDBC driver.
• DataSourceRealm?- Accesses authentication information stored in a relational database, accessed via a named JNDI JDBC DataSource.
• 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).
• JAASRealm?- Accesses authentication information through the Java Authentication & Authorization Service (JAAS) framework.

It is also possible to write your own?Realm?implementation, and integrate it with Tomcat 6. To do so, you need to:

• Implement?org.apache.catalina.Realm,
• Place your compiled realm in $CATALINA_HOME/lib,
• Declare your realm as described in the "Configuring a Realm" section below,
• Declare your realm to the?MBeans Descriptor.

?

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.xmlconfiguration file, that looks something like this:

The?<Realm>?element can be nested inside any one of of the following?Container?elements. The location of the Realm element has a direct impact on the "scope" of that Realm (i.e. which web applications will share the same authentication information):

• 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.

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 thejava.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 passwords 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.

If using digested passwords with DIGEST authentication, the cleartext used to generate the digest is different. In the examples above?{cleartext-password}?must be replaced with?{username}:{realm}:{cleartext-password}. For example, in a development environment this might take the form?testUser:localhost:8080:testPassword.

To use either of the above techniques, the?$CATALINA_HOME/lib/catalina.jar?and?$CATALINA_HOME/bin/tomcat-juli.jarfiles will need to be on your class path to make the?RealmBase?class available.

Non-ASCII usernames and/or passwords are supported using

?

The example application shipped with Tomcat 6 includes an area that is protected by a security constraint, utilizing form-based login. To access it, point your browser athttp://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 6 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.

Debugging and exception messages logged by a?Realm?will be recorded by the logging configuration associated with the container for the realm: its surrounding?Context,?Host, or?Engine.

Introduction

JDBCRealm?is an implementation of the Tomcat 6?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:

Realm Element Attributes

To configure JDBCRealm, you will create a?<Realm>?element and nest it in your?$CATALINA_BASE/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_BASE/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 6 will call theauthenticate()?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.

Introduction

DataSourceRealm?is an implementation of the Tomcat 6?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:

Realm Element Attributes

To configure DataSourceRealm, you will create a?<Realm>?element and nest it in your?$CATALINA_BASE/conf/server.xmlfile, 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 6 will call theauthenticate()?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.

Introduction

JNDIRealm?is an implementation of the Tomcat 6?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?andconnectionPassword?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 theuserBase?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 theroleBase?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. UseuserRoleName?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:

Realm Element Attributes

To configure JNDIRealm, you will create a?<Realm>?element and nest it in your?$CATALINA_BASE/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 fromhttp://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. Seehttp://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 asuid=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 6 will call theauthenticate()?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.

Introduction

MemoryRealm?is a simple demonstration implementation of the Tomcat 6?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_BASE/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_BASE/conf/server.xmlfile, 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 6 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.xmlfile 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 6 will call theauthenticate()?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.

Introduction

JAASRealm?is an implementation of the Tomcat 6?Realm?interface that authenticates users through the Java Authentication & Authorization Service (JAAS) framework which is now provided as part of the standard J2SE API.

Using JAASRealm gives the developer the ability to combine practically any conceivable security realm with Tomcat's CMA.

JAASRealm is prototype for Tomcat of the JAAS-based J2EE authentication framework for J2EE v1.4, based on theJCP Specification Request 196?to enhance container-managed security and promote 'pluggable' authentication mechanisms whose implementations would be container-independent.

Based on the JAAS login module and principal (see?javax.security.auth.spi.LoginModule?and?javax.security.Principal), you can develop your own security mechanism or wrap another third-party mechanism for integration with the CMA as implemented by Tomcat.

Quick Start

To set up Tomcat to use JAASRealm with your own JAAS login module, you will need to follow these steps:

Realm Element Attributes

To configure JAASRealm as for step 6 above, you create a?<Realm>?element and nest it in your$CATALINA_BASE/conf/server.xml?file within your?<Engine>?node. The following attributes are supported by this implementation:

Example

Here is an example of how your server.xml snippet should look.

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

The flexibility of the JAAS approach is two-fold:

• you can carry out whatever processing you require behind the scenes in your own login module.
• you can plug in a completely different LoginModule by changing the configuration and restarting the server, without any code changes to your application.

Additional Notes

• When a user attempts to access a protected resource for the first time, Tomcat 6 will call theauthenticate()?method of this?Realm. Thus, any changes you have made in the security mechanism 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 security information for an already authenticated user will?not?be reflected until the next time that user logs on again.
• As with other?Realm?implementations, digested passwords are supported if the?<Realm>?element in?server.xmlcontains a?digest?attribute; JAASRealm's?CallbackHandler?will digest the password prior to passing it back to the?LoginModule

Introduction

CombinedRealm?is an implementation of the Tomcat 6?Realm?interface that authenticates users through one or more sub-Realms.

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

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

Realm Element Attributes

To configure a CombinedRealm, you create a?<Realm>?element and nest it in your?$CATALINA_BASE/conf/server.xml?file within your?<Engine>?or?<Host>. You can also nest inside a?<Context>?node in a?context.xml?file. The following attributes are supported by this implementation:

Example

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

Introduction

LockOutRealm?is an implementation of the Tomcat 6?Realm?interface that extends the CombinedRealm to provide lock out functionality to provide a user lock out mechanism if there are too many failed authentication attempts in a given period of time.

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

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

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

Realm Element Attributes

To configure a LockOutRealm, you create a?<Realm>?element and nest it in your?$CATALINA_BASE/conf/server.xml?file within your?<Engine>?or?<Host>. You can also nest inside a?<Context>?node in a?context.xml?file. The following attributes are supported by this implementation:

Example

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