Documentation Contents

# JAAS Authorization

This tutorial expands the program and policy file developed in the JAAS Authentication tutorial to demonstrate the JAAS authorization component, which ensures the authenticated caller has the access control rights (permissions) required to do subsequent security-sensitive operations. Since the authorization component requires that the user authentication first be completed, please read the JAAS Authentication tutorial first if you have not already done so.

The rest of this tutorial consists of the following sections:

- What is JAAS Authorization?
- How is JAAS Authorization Performed?
  - How Do You Make Principal-Based Policy File Statements?
  - How Do You Associate a Subject with an Access Control Context?
- The Authorization Tutorial Code
- The Login Configuration File
- The Policy File
- Running the Authorization Tutorial Code

If you want to first see the tutorial code in action, you can skip directly to Running the Authorization Tutorial Code and then go back to the other sections to learn more.

## What is JAAS Authorization?

JAAS authorization extends the existing Java security architecture that uses a security policy to specify what access rights are granted to executing code. That architecture, introduced in the Java 2 platform, is code-centric. That is, the permissions are granted based on code characteristics: where the code is coming from and whether it is digitally signed and if so by whom. We saw an example of this in the `jaasacn.policy` file used in the JAAS Authentication tutorial. That file contains the following:

    grant codebase "file:./JaasAcn.jar" {
       permission javax.security.auth.AuthPermission
                        "createLoginContext.JaasSample";
    };

This grants the code in the `JaasAcn.jar` file, located in the current directory, the specified permission. (No signer is specified, so it doesn't matter whether the code is signed or not.)

JAAS authorization augments the existing code-centric access controls with new user-centric access controls. Permissions can be granted based not just on what code is running but also on who is running it.

When an application uses JAAS authentication to authenticate the user (or other entity such as a service), a Subject is created as a result. The purpose of the Subject is to represent the authenticated user. A Subject is comprised of a set of Principals, where each Principal represents an identity for that user. For example, a Subject could have a name Principal ("Susan Smith") and a Social Security Number Principal ("987-65-4321"), thereby distinguishing this Subject from other Subjects.

Permissions can be granted in the policy to specific Principals. After the user has been authenticated, the application can associate the Subject with the current access control context. For each subsequent security-checked operation, (a local file access, for example), the Java runtime will automatically determine whether the policy grants the required permission only to a specific Principal and if so, the operation will be allowed only if the Subject associated with the access control context contains the designated Principal.

## How is JAAS Authorization Performed?

To make JAAS authorization take place, the following is required:

- The user must be authenticated, as described in the JAAS Authentication tutorial.
- Principal-based entries must be configured in the security policy.
- The Subject that is the result of authentication must be associated with the current access control context.

### How Do You Make Principal-Based Policy File Statements?

Policy file `grant` statements can now optionally include one or more Principal fields. Inclusion of a Principal field indicates that the user or other entity represented by the specified Principal, executing the specified code, has the designated permissions.

Thus, the basic format of a `grant` statement is now

    grant <signer(s) field>, <codeBase URL>
      <Principal field(s)> {
        permission perm_class_name "target_name", "action";
        ....
        permission perm_class_name "target_name", "action";
      };

where each of the signer, codeBase and Principal fields is optional and the order between the fields doesn't matter.

A Principal field looks like the following:

    Principal Principal_class "principal_name"

That is, it is the word "Principal" (where case doesn't matter) followed by the (fully qualified) name of a Principal class and a principal name.

A Principal class is a class that implements the java.security.Principal interface. All Principal objects have an associated name that can be obtained by calling their `getName` method. The format used for the name is dependent on each Principal implementation.

The type of Principal placed in the Subject created by the Kerberos authentication mechanism used by this tutorial is `javax.security.auth.kerberos.KerberosPrincipal`, so that is what should be used as the `Principal_class` part of our `grant` statement's Principal designation. User names for `KerberosPrincipal`s are of the form "name@realm". Thus, if the user name is "mjones" and the realm is "KRBNT-OPS.ABC.COM", the full `principal_name` designation to use in the `grant` statement is "mjones@KRBNT-OPS.ABC.COM".

It is possible to include more than one Principal field in a `grant` statement. If multiple Principal fields are specified, then the permissions in that `grant` statement are granted only if the Subject associated with the current access control context contains all of those Principals.

To grant the same set of permissions to different Principals, create multiple `grant` statements where each lists the permissions and contains a single Principal field designating one of the Principals.

The policy file for this tutorial includes one `grant` statement with a Principal field:

    grant codebase "file:./SampleAction.jar",
        Principal javax.security.auth.kerberos.KerberosPrincipal
            "your_user_name@your_realm"  {

       permission java.util.PropertyPermission "java.home", "read";
       permission java.util.PropertyPermission "user.home", "read";
       permission java.io.FilePermission "foo.txt", "read";
    };

where you substitute your Kerberos user name (complete with "@" and realm) for "`your_user_name@your_realm`".

This specifies that the indicated permissions are granted to the specified principal executing the code in `SampleAction.jar`.

### How Do You Associate a Subject with an Access Control Context?

To create and associate a Subject with an access control context, you need the following:

- The user must first be authenticated, as described in JAAS Authentication.
- The static `doAs` method from the Subject class must be called, passing it an authenticated Subject and a java.security.PrivilegedAction or java.security.PrivilegedExceptionAction. (See API for Privileged Blocks for a comparison of PrivilegedAction and PrivilegedExceptionAction.) The `doAs` method associates the provided Subject with the current access control context and then invokes the `run` method from the action. The `run` method implementation contains all the code to be executed as the specified Subject. The action thus executes as the specified Subject.

  The static `doAsPrivileged` method from the Subject class may be called instead of the `doAs` method. In addition to the parameters passed to `doAs`, `doAsPrivileged` requires a third parameter: an AccessControlContext. Unlike `doAs`, which associates the provided Subject with the current access control context, `doAsPrivileged` associates the Subject with the provided access control context. See doAs vs. doAsPrivileged in the JAAS Reference Guide for a comparison of those methods.

## The Authorization Tutorial Code

The code for this tutorial consists of two files:

- JaasAzn.java is exactly the same as the `JaasAcn.java` from the JAAS Authentication tutorial except for the additional code needed to call `Subject.doAsPrivileged`.
- SampleAction.java contains the SampleAction class. This class implements PrivilegedAction and has a `run` method that contains all the code we want to be executed with Principal-based authorization checks.

### JaasAzn.java

JaasAzn.java is exactly the same as the `JaasAcn.java` code used in the previous tutorial except with three statements added at the end of the `main` method, after the authentication is done. These statements result in (1) association of a Subject representing the authenticated user with the current access control context and (2) execution of the code in the `run` method of SampleAction. Associating the Subject with the access control context enables security-sensitive operations in the SampleAction `run` method (and any code it invokes directly or indirectly) to be executed if a Principal representing the authenticated user is granted the required permissions in the current policy.

Like `JaasAcn.java`, `JaasAzn.java` instantiates a LoginContext `lc` and calls its `login` method to perform the authentication. If successful, the authenticated Subject (which includes a Principal representing the user) is obtained by calling the LoginContext's `getSubject` method:

    Subject mySubject = lc.getSubject();

The `main` method then calls `Subject.doAsPrivileged`, passing it the authenticated Subject `mySubject`, a PrivilegedAction (SampleAction) and a `null` AccessControlContext, as described in the following.

The SampleAction class is instantiated via the following:

    PrivilegedAction action = new SampleAction();

The call to `Subject.doAsPrivileged` is performed via:

    Subject.doAsPrivileged(mySubject, action, null);

The `doAsPrivileged` method invokes execution of the `run` method in the PrivilegedAction `action` (SampleAction) to initiate execution of the rest of the code, which is considered to be executed on behalf of the Subject `mySubject`.

Passing `null` as the AccessControlContext (third) argument to `doAsPrivileged` indicates that `mySubject` should be associated with a new empty AccessControlContext. The result is that security checks occurring during execution of SampleAction will only require permissions for the SampleAction code itself (or other code it invokes), running as `mySubject`. Note that the caller of `doAsPrivileged` (and the callers on the execution stack at the time `doAsPrivileged` was called) do not require any permissions while the action executes.

### SampleAction.java

SampleAction.java contains the SampleAction class. This class implements `java.security.PrivilegedAction` and has a `run` method that contains all the code we want to be executed as the Subject `mySubject`. For this tutorial, we will perform three operations, each of which cannot be done unless code has been granted required permissions. We will:

- Read and print the value of the `java.home` system property,
- Read and print the value of the `user.home` system property, and
- Determine whether or not a file named `foo.txt` exists in the current directory.

Here is the code:

    import java.io.File;
    import java.security.PrivilegedAction;

    public class SampleAction implements PrivilegedAction {

      public Object run() {

        System.out.println("\nYour java.home property value is: "
                    + System.getProperty("java.home"));

        System.out.println("\nYour user.home property value is: "
                    + System.getProperty("user.home"));

        File f = new File("foo.txt");
        System.out.print("\nfoo.txt does ");
        if (!f.exists())
            System.out.print("not ");
        System.out.println("exist in the current working directory.");
        return null;
      }
    }

## The Login Configuration File

The login configuration file used for this tutorial can be exactly the same as that used by the JAAS Authentication tutorial. Thus we can use jaas.conf, which contains just one entry:

    JaasSample {
      com.sun.security.auth.module.Krb5LoginModule required;
    };

This entry is named "JaasSample" and that is the name that both our tutorial applications `JaasAcn` and `JaasAzn` use to refer to it. The entry specifies that the LoginModule to be used to do the user authentication is the Krb5LoginModule in the `com.sun.security.auth.module` package and that this Krb5LoginModule is required to "succeed" in order for authentication to be considered successful. The Krb5LoginModule succeeds only if the name and password supplied by the user are successfully used to log the user into the Kerberos KDC.

## The Policy File

This authorization tutorial contains two classes, `JaasAzn` and `SampleAction`. The code in each class contains some security-sensitive operations and thus relevant permissions are required in a policy file in order for the operations to be executed.

### Permissions Required by JaasAzn

The main method of the `JaasAzn` class does two operations for which permissions are required. It

- creates a LoginContext, and
- calls the `doAsPrivileged` static method of the Subject class.

The LoginContext creation is exactly the same as was done in the authentication tutorial, and it thus needs the same `javax.security.auth.AuthPermission` permission with target "`createLoginContext.JaasSample`".

In order to call the `doAsPrivileged` method of the Subject class, you need to have a `javax.security.auth.AuthPermission` with target "`doAsPrivileged`".

Assuming the `JaasAzn` class is placed in a JAR file named `JaasAzn.jar`, these permissions can be granted to the `JaasAzn` code via the following `grant` statement in the policy file:

    grant codebase "file:./JaasAzn.jar" {
       permission javax.security.auth.AuthPermission
                        "createLoginContext.JaasSample";
       permission javax.security.auth.AuthPermission "doAsPrivileged";
    };

### Permissions Required by SampleAction

The `SampleAction` code does three operations for which permissions are required. It

- reads the value of the "java.home" system property.
- reads the value of the "user.home" system property.
- checks to see whether or not a file named `foo.txt` exists in the current directory.

The permissions required for these operations are the following:

    permission java.util.PropertyPermission "java.home", "read";
    permission java.util.PropertyPermission "user.home", "read";
    permission java.io.FilePermission "foo.txt", "read";

We need to grant these permissions to the code in `SampleAction.class`, which we will place in a JAR file named `SampleAction.jar`. However, for this particular `grant` statement we want to grant the permissions not just to the code but to a specific user executing the code, to demonstrate how to restrict access to a particular user.

Thus, as explained in How Do You Make Principal-Based Policy File Statements?, our `grant` statement looks like the following:

    grant codebase "file:./SampleAction.jar",
        Principal javax.security.auth.kerberos.KerberosPrincipal
            "your_user_name@your_realm"  {

       permission java.util.PropertyPermission "java.home", "read";
       permission java.util.PropertyPermission "user.home", "read";
       permission java.io.FilePermission "foo.txt", "read";
    };

You substitute your Kerberos user name (complete with "@" and realm) for "`your_user_name@your_realm`". For example, if your user name is "mjones" and your realm is "KRBNT-OPERATIONS.ABC.COM", you would use "mjones@KRBNT-OPERATIONS.ABC.COM" (complete with the quotes).

### The Full Policy File

The full policy file is jaasazn.policy.

## Running the Authorization Tutorial Code

To execute our JAAS authorization tutorial code, all you have to do is

1. Place the following files into a directory:
   - The JaasAzn.java source file.
   - The SampleAction.java source file.
   - The jaas.conf login configuration file.
   - The jaasazn.policy policy file.
2. Replace "your_user_name@your_realm" in `jaasazn.policy` with your user name and realm.
3. Compile `SampleAction.java` and `JaasAzn.java`:

       javac SampleAction.java JaasAzn.java

4. Create a JAR file named `JaasAzn.jar` containing `JaasAzn.class`:

       jar -cvf JaasAzn.jar JaasAzn.class

5. Create a JAR file named `SampleAction.jar` containing `SampleAction.class`:

       jar -cvf SampleAction.jar SampleAction.class

6. Execute the `JaasAzn` application, specifying
   1. by an appropriate `-classpath` clause that classes should be searched for in the `JaasAzn.jar` and `SampleAction.jar` JAR files,
   2. by `-Djava.security.manager` that a security manager should be installed,
   3. by `-Djava.security.krb5.realm=<your_realm>` that your Kerberos realm is the one specified.
   4. by `-Djava.security.krb5.kdc=<your_kdc>` that your Kerberos KDC is the one specified.
   5. by `-Djava.security.policy=jaasazn.policy` that the policy file to be used is `jaasazn.policy`, and
   6. by `-Djava.security.auth.login.config=jaas.conf` that the login configuration file to be used is `jaas.conf`.

   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 Windows systems you use semicolons to separate classpath items, while you use colons for that purpose on Solaris, Linux, and Mac OS X. Be sure to replace `<your_realm>` with your Kerberos realm, and `<your_kdc>` with your Kerberos KDC.

   Here is the full command for Windows systems:

       java -classpath JaasAzn.jar;SampleAction.jar
        -Djava.security.manager
        -Djava.security.krb5.realm=<your_realm>
        -Djava.security.krb5.kdc=<your_kdc>
        -Djava.security.policy=jaasazn.policy
        -Djava.security.auth.login.config=jaas.conf JaasAzn

   Here is the full command for Solaris, Linux, and Mac OS X systems:

       java -classpath JaasAzn.jar:SampleAction.jar
        -Djava.security.manager
        -Djava.security.krb5.realm=<your_realm>
        -Djava.security.krb5.kdc=<your_kdc>
        -Djava.security.policy=jaasazn.policy
        -Djava.security.auth.login.config=jaas.conf JaasAzn

   Type the full command 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 Windows) or a .sh file (for Solaris, Linux, and Mac OS X) and then run that file to execute the command.

   You will be prompted for your Kerberos user name and password, and the underlying Kerberos authentication mechanism specified in the login configuration file will log you into Kerberos. If your login is successful, you will see the message "Authentication succeeded!" and if not, you will see "Authentication Failed."

   For login troubleshooting suggestions, see Troubleshooting.

   Once authentication is successfully completed, the rest of the program (in `SampleAction`) will be executed on behalf of you, the user, requiring you to have been granted appropriate permissions. The `jaasazn.policy` policy file grants you the required permissions, so you will see a display of the values of your `java.home` and `user.home` system properties and a statement as to whether or not you have a file named `foo.txt` in the current directory.

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