The Java Authentication and Authorization Service (JAAS) was introduced as an optional package in Java SE 1.3. JAAS was integrated into the JDK starting with JDK 1.4.
JAAS can be used for two purposes:
This section provides a basic tutorial for the authentication component. The authorization component will be described in the JAAS Authorization Tutorial.
JAAS authentication is performed in a pluggable fashion. This permits Java applications to remain independent from underlying authentication technologies. New or updated technologies can be plugged in without requiring modifications to the application itself. An implementation for a particular authentication technology to be used is determined at runtime. The implementation is specified in a login configuration file. The authentication technology used for this tutorial is very basic, just ensuring that the user specifies a particular name and password.
The rest of this tutorial consists of the following sections:
If you want to first see the tutorial code in action, you can skip directly to Running the Code and then go back to the other sections to learn about coding and configuration file details.
The code for this tutorial consists of three files:
Our authentication tutorial application code is contained in a single source file, SampleAcn.java. That file contains two classes:
main method of the SampleAcn class performs the
authentication and then reports whether or not authentication
succeeded.
The code for authenticating the user is very simple, consisting of just two steps:
First the basic code is shown, followed by a complete listing of the SampleAcn
class, complete with the import statement it requires and error
handling.
In order to authenticate a user, you first need a
javax.security.auth.login.LoginContext. Here is the
basic way to instantiate a LoginContext:
import javax.security.auth.login.*;
. . .
LoginContext lc =
new LoginContext(<config file entry name>,
<CallbackHandler to be used for user interaction>);
and here is the specific way our tutorial code does the
instantiation:
import javax.security.auth.login.*;
. . .
LoginContext lc =
new LoginContext("Sample",
new MyCallbackHandler());
The arguments are the following:
This is the name for the LoginContext to use to look up an entry
for this application in the JAAS login configuration file,
described here. Such an entry specifies
the class(es) that implement the desired underlying authentication
technology(ies). The class(es) must implement the LoginModule
interface, which is in the javax.security.auth.spi
package.
In our sample code, we use the SampleLoginModule
supplied with this tutorial. The SampleLoginModule performs
authentication by ensuring that the user types a particular name
and password.
The entry in the login configuration file we use for this tutorial (see sample_jaas.config) has the name "Sample", so that is the name we specify as the first argument to the LoginContext constructor.
When a LoginModule needs to communicate with the user, for
example to ask for a user name and password, it does not do so
directly. That is because there are various ways of communicating
with a user, and it is desirable for LoginModules to remain
independent of the different types of user interaction. Rather, the
LoginModule invokes a
javax.security.auth.callback.CallbackHandler to
perform the user interaction and obtain the requested information,
such as the user name and password.
An instance of the particular CallbackHandler to be used is
specified as the second argument to the LoginContext constructor.
The LoginContext forwards that instance to the underlying
LoginModule (in our case SampleLoginModule). An application
typically provides its own CallbackHandler implementation. A
simple CallbackHandler, TextCallbackHandler, is provided in the
com.sun.security.auth.callback package to output
information to and read input from the command line. However, we
instead demonstrate the more typical case of an application
providing its own CallbackHandler implementation, described in
The MyCallbackHandler Class.
login MethodOnce we have a LoginContext lc, we can call its
login method to carry out the authentication
process:
lc.login();
The LoginContext instantiates a new empty javax.security.auth.Subject
object (which represents the user or service being authenticated).
The LoginContext constructs the configured LoginModule (in our case
SampleLoginModule) and initializes it with this new Subject and
MyCallbackHandler.
The LoginContext's login method then calls methods
in the SampleLoginModule to perform the login and authentication.
The SampleLoginModule will utilize the MyCallbackHandler to obtain
the user name and password. Then the SampleLoginModule will check
that the name and password are the ones it expects.
If authentication is successful, the SampleLoginModule populates the Subject with a Principal representing the user. The Principal the SampleLoginModule places in the Subject is an instance of SamplePrincipal, which is a sample class implementing the java.security.Principal interface.
See Subjects, Principals, Authentication, and Credentials for information on these terms.
The calling application can subsequently retrieve the
authenticated Subject by calling the LoginContext's
getSubject method, although doing so is not necessary
for this tutorial.
SampleAcn Class CodeNow that you have seen the basic code required to authenticate the user, we can put it all together into the full class in SampleAcn.java, which includes relevant import statements and error handling:
package sample;
import javax.security.auth.login.*;
// . . . other import statements needed by MyCallbackHandler . . .
/**
* This Sample application attempts to authenticate a user
* and reports whether or not the authentication was
* successful.
*/
public class SampleAcn {
/**
* Attempt to authenticate the user.
*
* @param args input arguments for this application.
* These are ignored.
*/
public static void main(String[] args) {
// Obtain a LoginContext, needed for authentication.
// Tell it to use the LoginModule implementation
// specified by the entry named "Sample" in the
// JAAS login configuration file and to also use the
// specified CallbackHandler.
LoginContext lc = null;
try {
lc = new LoginContext("Sample",
new MyCallbackHandler());
} catch (LoginException le) {
System.err.println("Cannot create LoginContext. "
+ le.getMessage());
System.exit(-1);
} catch (SecurityException se) {
System.err.println("Cannot create LoginContext. "
+ se.getMessage());
System.exit(-1);
}
// the user has 3 attempts to authenticate successfully
int i;
for (i = 0; i < 3; i++) {
try {
// attempt authentication
lc.login();
// if we return with no exception,
// authentication succeeded
break;
} catch (LoginException le) {
System.err.println("Authentication failed:");
System.err.println(" " + le.getMessage());
try {
Thread.currentThread().sleep(3000);
} catch (Exception e) {
// ignore
}
}
}
// did they fail three times?
if (i == 3) {
System.out.println("Sorry");
System.exit(-1);
}
System.out.println("Authentication succeeded!");
}
}
In some cases a LoginModule must communicate with the user to
obtain authentication information. LoginModules use a
javax.security.auth.callback.CallbackHandler for
this purpose. An application can either use one of the sample
implementations provided in the
com.sun.security.auth.callback package or, more
typically, write a CallbackHandler implementation. The application
passes the CallbackHandler as an argument to the LoginContext
instantiation. The LoginContext forwards the CallbackHandler
directly to the underlying LoginModules.
The tutorial sample code supplies its own CallbackHandler implementation, the MyCallbackHandler class in SampleAcn.java.
CallbackHandler is an interface with one method to implement:
void handle(Callback[] callbacks)
throws java.io.IOException, UnsupportedCallbackException;
The LoginModule passes the CallbackHandler handle method an
array of appropriate
javax.security.auth.callback.Callbacks, for example a
NameCallback for the user name and a
PasswordCallback for the password, and the CallbackHandler
performs the requested user interaction and sets appropriate values
in the Callbacks.
The MyCallbackHandler handle method is structured
as follows:
public void handle(Callback[] callbacks)
throws IOException, UnsupportedCallbackException {
for (int i = 0; i < callbacks.length; i++) {
if (callbacks[i] instanceof TextOutputCallback) {
// display a message according to a specified type
. . .
} else if (callbacks[i] instanceof NameCallback) {
// prompt the user for a username
. . .
} else if (callbacks[i] instanceof PasswordCallback) {
// prompt the user for a password
. . .
} else {
throw new UnsupportedCallbackException
(callbacks[i], "Unrecognized Callback");
}
}
}
A CallbackHandler handle method is passed an array
of Callback instances, each of a particular type (NameCallback,
PasswordCallback, etc.). It must handle each Callback, performing
user interaction in a way that is appropriate for the executing
application.
MyCallbackHandler handles three types of Callbacks: NameCallback to prompt the user for a user name, PasswordCallback to prompt for a password, and TextOutputCallback to report any error, warning, or other messages the SampleLoginModule wishes to send to the user.
The handle method handles a
TextOutputCallback by extracting the message to be reported
and then printing it to System.out, optionally
preceded by additional wording that depends on the message type.
The message to be reported is determined by calling the
TextOutputCallback's getMessage method and the type by
calling its getMessageType method. Here is the code
for handling a TextOutputCallback:
if (callbacks[i] instanceof TextOutputCallback) {
// display the message according to the specified type
TextOutputCallback toc = (TextOutputCallback)callbacks[i];
switch (toc.getMessageType()) {
case TextOutputCallback.INFORMATION:
System.out.println(toc.getMessage());
break;
case TextOutputCallback.ERROR:
System.out.println("ERROR: " + toc.getMessage());
break;
case TextOutputCallback.WARNING:
System.out.println("WARNING: " + toc.getMessage());
break;
default:
throw new IOException("Unsupported message type: " +
toc.getMessageType());
}
The handle method handles a NameCallback by
prompting the user for a user name. It does this by printing the
prompt to System.err. It then sets the name for use by
the SampleLoginModule by calling the NameCallback's
setName method, passing it the name typed by the
user:
} else if (callbacks[i] instanceof NameCallback) {
// prompt the user for a username
NameCallback nc = (NameCallback)callbacks[i];
System.err.print(nc.getPrompt());
System.err.flush();
nc.setName((new BufferedReader
(new InputStreamReader(System.in))).readLine());
Similarly, the handle method handles a
PasswordCallback by printing a prompt to
System.err to prompt the user for a password. It then
sets the password for use by the SampleLoginModule by calling the
PasswordCallback's setPassword method, passing it the
password typed by the user, which it reads by calling the
readPassword method (shown below):
} else if (callbacks[i] instanceof PasswordCallback) {
// prompt the user for sensitive information
PasswordCallback pc = (PasswordCallback)callbacks[i];
System.err.print(pc.getPrompt());
System.err.flush();
pc.setPassword(readPassword(System.in));
The readPassword method is a basic method for
reading a password from an InputStream:
private char[] readPassword(InputStream in) throws IOException {
char[] lineBuffer;
char[] buf;
int i;
buf = lineBuffer = new char[128];
int room = buf.length;
int offset = 0;
int c;
loop:
while (true) {
switch (c = in.read()) {
case -1:
case '\n':
break loop;
case '\r':
int c2 = in.read();
if ((c2 != '\n') && (c2 != -1)) {
if (!(in instanceof PushbackInputStream)) {
in = new PushbackInputStream(in);
}
((PushbackInputStream)in).unread(c2);
} else
break loop;
default:
if (--room < 0) {
buf = new char[offset + 128];
room = buf.length - offset - 1;
System.arraycopy(lineBuffer, 0, buf, 0, offset);
Arrays.fill(lineBuffer, ' ');
lineBuffer = buf;
}
buf[offset++] = (char) c;
break;
}
}
if (offset == 0) {
return null;
}
char[] ret = new char[offset];
System.arraycopy(buf, 0, ret, 0, offset);
Arrays.fill(buf, ' ');
return ret;
}
}
SampleLoginModule.java
implements the
LoginModule interface. SampleLoginModule is the class
specified by the tutorial's login
configuration file as the class implementing the desired
underlying authentication. SampleLoginModule's user authentication
consists of simply verifying that the name and password specified
by the user have specific values. This SampleLoginModule is
specified by the tutorial's login configuration file as the
LoginModule to use because (1) It performs a basic type of
authentication suitable for any environment and thus is appropriate
for a tutorial for all users, and (2) It provides an example
LoginModule implementation for experienced programmers who require
the ability to write a LoginModule implementing an authentication
technology.
SamplePrincipal.java is a sample class implementing the java.security.Principal interface. If authentication is successful, the SampleLoginModule populates a Subject with a SamplePrincipal representing the user.
Important: If you are an application writer, you do not need to know how to write a LoginModule or a Principal implementation. You do not need to examine the SampleLoginModule or SamplePrincipal code. All you have to know is how to write your application and specify configuration information (such as in a login configuration file) such that the application will be able to utilize the LoginModule specified by the configuration to authenticate the user. You need to determine which LoginModule(s) you want to use and read the LoginModule's documentation to learn about what options you can specify values for (in the configuration) to control the LoginModule's behavior.
Any vendor can provide a LoginModule implementation that you can use. Some implementations are supplied with the JRE from Sun Microsystems, as listed in the JAAS Login Configuration File document.
Information for programmers who want to write a LoginModule can
be found in the JAAS
LoginModule Developer's Guide.
JAAS authentication is performed in a pluggable fashion, so
applications can remain independent from underlying authentication
technologies. A system administrator determines the authentication
technologies, or LoginModules, to be used for each application and
configures them in a login Configuration. The source of the
configuration information (for example, a file or a database) is up
to the current javax.security.auth.login.Configuration
implementation. The default Configuration
implementation from Sun Microsystems reads configuration
information from configuration files, as described in
com.sun.security.auth.login.ConfigFile.html.
See JAAS Login Configuration File for information as to what a login configuration file is, what it contains, and how to specify which login configuration file should be used.
As noted, the login configuration file we use for this tutorial, sample_jaas.config, contains just one entry, which is
Sample {
sample.module.SampleLoginModule required debug=true;
};
This entry is named "Sample" and that is the name that our
tutorial application, SampleAcn, uses to refer to this
entry. The entry specifies that the LoginModule to be used to do
the user authentication is the SampleLoginModule in the
sample.module package and that this SampleLoginModule
is required to "succeed" in order for authentication to be
considered successful. The SampleLoginModule succeeds only if the
name and password supplied by the user are the one it expects
("testUser" and "testPassword", respectively).
The SampleLoginModule also defines a "debug" option that can be
set to true as shown. If this option is set to
true, SampleLoginModule outputs extra information
about the progress of authentication. A LoginModule can define as
many options as it wants. The LoginModule documentation should
specify the possible option names and values you can set in your
configuration file.
To execute our JAAS authentication tutorial code, all you have to do is
SampleAcn.java, are
in a package named sample):
sample.module):
sample.principal):
SampleAcn.java, SampleLoginModule.java,
and SamplePrincipal.java:
javac sample/SampleAcn.java sample/module/SampleLoginModule.java sample/principal/SamplePrincipal.java(Type all that on one line.)
SampleAcn application, specifying
-Djava.security.auth.login.config==sample_jaas.config
that the login configuration file to be used is
sample_jaas.config.The full command is below.
java -Djava.security.auth.login.config==sample_jaas.config sample.SampleAcn
You will be prompted for your user name and password, and the SampleLoginModule specified in the login configuration file will check to ensure these are correct. The SampleLoginModule expects "testUser" for the user name and "testPassword" for the password.
You will see some messages output by SampleLoginModule as a
result of the debug option being set to
true in the login configuration file. Then, if your
login is successful, you will see the following message output by
SampleAcn:
Authentication succeeded!If the login is not successful (for example, if you misspell the password), you will see
Authentication failed:followed by a reason for the failure. For example, if you mistype the password, you may see a message like the following:
Authentication failed: Password Incorrect
SampleAcn gives you three chances to successfully log in.
When a Java program is run with a security manager installed, the program is not allowed to access resources or otherwise perform security-sensitive operations unless it is explicitly granted permission to do so by the security policy in effect. The permission must be granted by an entry in a policy file.
Most browsers install a security manager, so applets
typically run under the scrutiny of a security manager.
Applications, on the other hand, do not, since a security
manager is not automatically installed when an application is
running. Thus an application, like our SampleAcn
application, by default has full access to resources.
To run an application with a security manager, simply
invoke the interpreter with a -Djava.security.manager
argument included on the command line.
If you try invoking SampleAcn with a security
manager but without specifying any policy file, you will get the
following (unless you have a default policy setup elsewhere that
grants the required permissions or grants
AllPermission):
% java -Djava.security.manager \ -Djava.security.auth.login.config==sample_jaas.config sample.SampleAcn Exception in thread "main" java.security.AccessControlException: access denied ( javax.security.auth.AuthPermission createLoginContext.Sample)
As you can see, you get an AccessControlException, because we haven't created and used a policy file granting our code the permission that is required in order to be allowed to create a LoginContext.
Here are the complete steps required in order to be able to run
our SampleAcn application with a security manager
installed. You can skip the first five steps if you have already
done them, as described in Running the
Code.
SampleAcn.java, are
in a package named sample):
sample.module):
sample.principal):
SampleAcn.java, SampleLoginModule.java,
and SamplePrincipal.java:
javac sample/SampleAcn.java sample/module/SampleLoginModule.java sample/principal/SamplePrincipal.java(Type all that on one line.)
SampleAcn.class and
MyCallbackHandler.class:
jar -cvf SampleAcn.jar sample/SampleAcn.class sample/MyCallbackHandler.class
(Type all that on one line.) This command creates a JAR file,
SampleAcn.jar, and places the
SampleAcn.class and
MyCallbackHandler.class files inside it.
SampleLoginModule.class and
SamplePrincipal.class:
jar -cvf SampleLM.jar sample/module/SampleLoginModule.class sample/principal/SamplePrincipal.class
The permission that is needed by code attempting to instantiate
a LoginContext is a javax.security.auth.AuthPermission
with target "createLoginContext.<entry name>". Here,
<entry name> refers to the name of the login configuration
file entry that the application references in its instantiation of
LoginContext. The name used by our SampleAcn
application's LoginContext instantiation is "Sample", as you can
see in the code:
LoginContext lc =
new LoginContext("Sample",
new MyCallbackHandler());
Thus, the permission that needs to be granted to
SampleAcn.jar is
permission javax.security.auth.AuthPermission "createLoginContext.Sample";
The SampleLM.jar file also needs to be granted a
permission. The documentation for a LoginModule should tell you
what permissions it needs to be granted. In the case of
SampleLoginModule, it needs a
javax.security.auth.AuthPermission with target
"modifyPrincipals" in order to populate a Subject with a
Principal:
permission javax.security.auth.AuthPermission "modifyPrincipals";
Copy the policy file sampleacn.policy to the same directory as
that in which you stored SampleAcn.java, etc. The
policy file contains the following grant statement to
grant SampleAcn.jar (in the current directory) its
required permission:
grant codebase "file:./SampleAcn.jar" {
permission javax.security.auth.AuthPermission
"createLoginContext.Sample";
};
The policy file also contains the following grant
statement to grant SampleLM.jar (also in the current
directory) its required permission:
grant codebase "file:./SampleLM.jar" {
permission javax.security.auth.AuthPermission
"modifyPrincipals";
};
Note: Policy files and the structure of entries within them are described in Default Policy Implementation and Policy File Syntax. Permissions are described here.
SampleAcn application, specifying
-classpath clause that classes
should be searched for in the SampleAcn.jar and
SampleLM.jar JAR files,-Djava.security.manager that a security manager
should be installed,-Djava.security.policy==sampleacn.policy that
the policy file to be used is sampleacn.policy,
and-Djava.security.auth.login.config==sample_jaas.config
that the login configuration file to be used is
sample_jaas.config.Below are the full commands to use for both Microsoft Windows and Solaris, Linux, and Mac OS X systems. The only difference is that on Microsoft Windows systems you use semicolons to separate classpath items, while you use colons for that purpose on Solaris, Linux, and Mac OS X systems.
Here is the full command for Microsoft Windows systems:
java -classpath SampleAcn.jar;SampleLM.jar -Djava.security.manager -Djava.security.policy==sampleacn.policy \ -Djava.security.auth.login.config==sample_jaas.config \ sample.SampleAcn
Here is the full command for Solaris, Linux, and Mac OS X systems:
java -classpath SampleAcn.jar:SampleLM.jar -Djava.security.manager -Djava.security.policy==sampleacn.policy \ -Djava.security.auth.login.config==sample_jaas.config \ sample.SampleAcn
Type all that on one line. Multiple lines are used here for legibility. If the command is too long for your system, you may need to place it in a .bat file (for Microsoft Windows) or a .sh file (for Solaris, Linux, and Mac OS X) and then run that file to execute the command.
Since the specified policy file contains an entry granting the code the required permissions, execution should proceed without any exceptions indicating a required permission was not granted. You will be prompted for a user name and password (use "testUser" and "testPassword"), and the SampleLoginModule specified in the login configuration file will check the name and password. If your login is successful, you will see the message "Authentication succeeded!" and if not, you will see "Authentication failed:" followed by a reason for the failure.
