Realm Configuration HOW-TO

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Apache Tomcat Development

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 2.4)
, Section 12.

For information about utilizing the Single Sign On feature of
Tomcat (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 desirable to “connect”
a servlet container to some existing authentication database or mechanism
that already exists in the production environment. Therefore, Tomcat
defines a Java interface (org.apache.catalina.Realm) that
can be implemented by “plug in” components to establish this connection.
Six standard plug-ins are provided, supporting connections to various
sources of authentication information:

  • 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.
  • UserDatabaseRealm – Accesses authentication
    information stored in an UserDatabase JNDI resource, which is typically
    backed by an XML document (conf/tomcat-users.xml).
  • 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. 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 Descriptors.
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 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.
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 undesirable because casual observers of the
authentication data can collect enough information to log on
successfully, and impersonate other users. To avoid this problem, the
standard implementations support the concept of 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
    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

    CATALINA_HOME/bin/digest.[bat|sh] -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 and the digest must use the MD5
algorithm. 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:Authentication required:testPassword. The value for
{realm} is taken from the <realm-name>
element of the web application’s <login-config>. If
not specified in web.xml, the default value of Authentication
required
is used.

Non-ASCII usernames and/or passwords are supported using

CATALINA_HOME/bin/digest.[bat|sh] -a {algorithm} -e {encoding} {input}

but care is required to ensure that the non-ASCII input is
correctly passed to the digester.
The digester returns {input}:{digest}. If the input appears
corrupted in the return, the digest will be invalid.

Manager Application

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

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

Realm Logging

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.

Standard Realm Implementations
JDBCRealm

Introduction

JDBCRealm is an implementation of the Tomcat
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/lib directory.
    Note that only JAR files are recognized!
  4. Set up a <Realm> element, as described below, in your
    $CATALINA_BASE/conf/server.xml file.
  5. Restart Tomcat if it is already running.

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 attributes for the
JDBCRealm are defined in the Realm configuration
documentation.

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_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”:


<Realm className="org.apache.catalina.realm.JDBCRealm"
      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 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.
DataSourceRealm

Introduction

DataSourceRealm is an implementation of the Tomcat
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.
    Be sure to set the Realm‘s localDataSource
    attribute appropriately, depending on where the JNDI DataSource is
    defined.
  4. Set up a <Realm> element, as described below, in your
    $CATALINA_BASE/conf/server.xml file.
  5. Restart Tomcat if it is already running.

Realm Element Attributes

To configure DataSourceRealm, you will create a <Realm>
element and nest it in your $CATALINA_BASE/conf/server.xml file,
as described above. The attributes for the
DataSourceRealm are defined in the Realm
configuration documentation.

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"
   dataSourceName="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 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.
JNDIRealm

Introduction

JNDIRealm is an implementation of the Tomcat
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 and/or “{2}” for an attribute from user’s directory entry,
      of the authenticated user. Use userRoleAttribute to
      specify the name of the attribute that provides the value for “{2}”.
    • roleName – the attribute in a role entry
      containing the name of that role.
    • roleNested – enable nested roles. Set to
      true if you want to nest roles in roles. If configured, then
      every newly found roleName and distinguished
      Name will be recursively tried for a new role search.
      The default value is false.
  • 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. Set up a <Realm> element, as described below, in your
    $CATALINA_BASE/conf/server.xml file.
  4. Restart Tomcat if it is already running.

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 attributes for the
JNDIRealm are defined in the Realm configuration
documentation.

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
https://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://docs.oracle.com/javase/7/docs/technotes/guides/jndi/index.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 a user entry for Janet Jones
dn: uid=jjones,ou=people,dc=mycompany,dc=com
objectClass: inetOrgPerson
uid: jjones
sn: jones
cn: janet jones
mail: j.jones@mycompany.com
userPassword: janet

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

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

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

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

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"
     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.

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"
     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"
    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 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.
UserDatabaseRealm

Introduction

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

Realm Element Attributes

To configure UserDatabaseRealm, you will create a <Realm>
element and nest it in your $CATALINA_BASE/conf/server.xml file,
as described above. The attributes for the
UserDatabaseRealm are defined in the Realm
configuration documentation.

User File Format

The users file uses the same format as the
MemoryRealm.

Example

The default installation of Tomcat is configured with a UserDatabaseRealm
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

UserDatabaseRealm 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 made to the data in
    this file will not be recognized until Tomcat is
    restarted. Changes may be made via the UserDatabase resource. Tomcat
    provides MBeans that may be accessed via JMX for this purpose.
  • When a user attempts to access a protected resource for the first time,
    Tomcat 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.
MemoryRealm

Introduction

MemoryRealm is a simple demonstration implementation of the
Tomcat 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.xml file,
as described above. The attributes for the
MemoryRealm are defined in the Realm
configuration documentation.

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.

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 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.
JAASRealm

Introduction

JAASRealm is an implementation of the Tomcat
Realm interface that authenticates users through the Java
Authentication & Authorization Service (JAAS) framework which is now
provided as part of the standard Java SE 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 the JCP 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:

  1. Write your own LoginModule, User and Role classes based
    on JAAS (see

    the JAAS Authentication Tutorial
    and

    the JAAS Login Module Developer’s Guide
    ) to be managed by the JAAS Login
    Context (javax.security.auth.login.LoginContext)
    When developing your LoginModule, note that JAASRealm’s built-in CallbackHandler
    only recognizes the NameCallback and PasswordCallback at present.
  2. Although not specified in JAAS, you should create
    separate classes to distinguish between users and roles, extending javax.security.Principal,
    so that Tomcat can tell which Principals returned from your login
    module are users and which are roles (see org.apache.catalina.realm.JAASRealm).
    Regardless, the first Principal returned is always treated as the user Principal.
  3. Place the compiled classes on Tomcat’s classpath
  4. Set up a login.config file for Java (see
    JAAS LoginConfig file
    ) and tell Tomcat where to find it by specifying
    its location to the JVM, for instance by setting the environment
    variable: JAVA_OPTS=$JAVA_OPTS -Djava.security.auth.login.config==$CATALINA_BASE/conf/jaas.config
  5. Configure your security-constraints in your web.xml for
    the resources you want to protect
  6. Configure the JAASRealm module in your server.xml
  7. Restart Tomcat if it is already running.

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 attributes for the
JAASRealm are defined in the Realm
configuration documentation.

Example

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


<Realm className="org.apache.catalina.realm.JAASRealm"
                appName="MyFooRealm"
    userClassNames="org.foobar.realm.FooUser"
     roleClassNames="org.foobar.realm.FooRole"/>

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 will call the authenticate()
    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.xml
    contains a digest attribute; JAASRealm’s CallbackHandler
    will digest the password prior to passing it back to the LoginModule
CombinedRealm

Introduction

CombinedRealm is an implementation of the Tomcat
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.

Example

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


<Realm className="org.apache.catalina.realm.CombinedRealm" >
   <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
             resourceName="UserDatabase"/>
   <Realm className="org.apache.catalina.realm.DataSourceRealm"
             dataSourceName="jdbc/authority"
             userTable="users" userNameCol="user_name" userCredCol="user_pass"
             userRoleTable="user_roles" roleNameCol="role_name"/>
</Realm>
LockOutRealm

Introduction

LockOutRealm is an implementation of the Tomcat
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 mechanisms. It achieves this by recording all failed
logins, including those for users that do not exist. To prevent a DOS by
deliberating making requests with invalid users (and hence causing this
cache to grow) the size of the list of users that have failed authentication
is limited.

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 attributes for the
LockOutRealm are defined in the Realm
configuration documentation.

Example

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


<Realm className="org.apache.catalina.realm.LockOutRealm" >
   <Realm className="org.apache.catalina.realm.UserDatabaseRealm"
             resourceName="UserDatabase"/>
</Realm>

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