OWASP Cheat Sheet Series: JAAS Cheat Sheet

# JAAS Cheat Sheet

## Introduction - What is JAAS authentication

The process of verifying the identity of a user or another system is authentication.

[JAAS](https://docs.oracle.com/javase/8/docs/technotes/guides/security/jaas/JAASRefGuide.html), as an authentication framework manages the authenticated user's identity and credentials from login to logout.

The JAAS authentication lifecycle:

1. Create `LoginContext`.
2. Read the configuration file for one or more `LoginModules` to initialize.
3. Call `LoginContext.initialize()` for each LoginModule to initialize.
4. Call `LoginContext.login()` for each LoginModule.
5. If login successful then call `LoginContext.commit()` else call `LoginContext.abort()`

## Configuration file

The JAAS configuration file contains a `LoginModule` stanza for each `LoginModule` available for logging on to the application.

A stanza from a JAAS configuration file:

```text
Branches
{
    USNavy.AppLoginModule required
    debug=true
    succeeded=true;
}
```

Note the placement of the semicolons, terminating both `LoginModule` entries and stanzas.

The word required indicates the `LoginContext`'s `login()` method must be successful when logging in the user. The `LoginModule`-specific values `debug` and `succeeded` are passed to the `LoginModule`.

They are defined by the `LoginModule` and their usage is managed inside the `LoginModule`. Note, Options are Configured using key-value pairing such as `debug="true"` and the key and value should be separated by a `=` sign.

## Main.java (The client)

- Execution syntax:

```text
Java –Djava.security.auth.login.config==packageName/packageName.config
        packageName.Main Stanza1

Where:
    packageName is the directory containing the config file.
    packageName.config specifies the config file in the Java package, packageName.
    packageName.Main specifies Main.java in the Java package, packageName.
    Stanza1 is the name of the stanza Main() should read from the config file.
```

- When executed, the 1st command-line argument is the stanza from the config file. The Stanza names the `LoginModule` to be used. The 2nd argument is the `CallbackHandler`.
- Create a new `LoginContext` with the arguments passed to `Main.java`.
    - `loginContext = new LoginContext (args[0], new AppCallbackHandler());`
- Call the LoginContext.Login Module:
    - `loginContext.login();`
- The value in succeeded Option is returned from `loginContext.login()`.
- If the login was successful, a subject was created.

## LoginModule.java

A `LoginModule` must have the following authentication methods:

- `initialize()`
- `login()`
- `commit()`
- `abort()`
- `logout()`

### initialize()

In `Main()`, after the `LoginContext` reads the correct stanza from the config file, the `LoginContext` instantiates the `LoginModule` specified in the stanza.

- `initialize()` methods signature:
    - `Public void initialize (Subject subject, CallbackHandler callbackHandler, Map sharedState, Map options)`
- The arguments above should be saved as follows:
    - `this.subject = subject;`
    - `this.callbackHandler = callbackHandler;`
    - `this.sharedState = sharedState;`
    - `this.options = options;`
- What the `initialize()` method does:
    - Builds a subject object of the `Subject` class contingent on a successful `login()`.
    - Sets the `CallbackHandler` which interacts with the user to gather login information.
    - If a `LoginContext` specifies 2 or more LoginModules, which is legal, they can share information via a `sharedState` map.
    - Saves state information such as debug and succeeded in an options Map.

### login()

Captures user supplied login information. The code snippet below declares an array of two callback objects which, when passed to the `callbackHandler.handle` method in the `callbackHandler.java` program, will be loaded with a username and password provided interactively by the user:

```java
NameCallback nameCB = new NameCallback("Username");
PasswordCallback passwordCB = new PasswordCallback ("Password", false);
Callback[] callbacks = new Callback[] { nameCB, passwordCB };
callbackHandler.handle (callbacks);
```

- Authenticates the user
- Retrieves the user supplied information from the callback objects:
    - `String ID = nameCallback.getName ();`
    - `char[] tempPW = passwordCallback.getPassword ();`
- Compare `name` and `tempPW` to values stored in a repository such as LDAP.
- Set the value of the variable succeeded and return to `Main()`.

### commit()

Once the users credentials are successfully verified during `login()`, the JAAS authentication framework associates the credentials, as needed, with the subject.

There are two types of credentials, **Public** and **Private**:

- Public credentials include public keys.
- Private credentials include passwords and public keys.

Principals (i.e. Identities the subject has other than their login name) such as employee number or membership ID in a user group are added to the subject.

Below, is an example `commit()` method where first, for each group the authenticated user has membership in, the group name is added as a principal to the subject. The subject's username is then added to their public credentials.

Code snippet setting then adding any principals and a public credentials to a subject:

```java
public boolean commit() {
    If (userAuthenticated) {
        Set groups = UserService.findGroups (username);
        for (Iterator itr = groups.iterator (); itr.hasNext (); {
            String groupName = (String) itr.next ();
            UserGroupPrincipal group = new UserGroupPrincipal (GroupName);
            subject.getPrincipals ().add (group);
        }
        UsernameCredential cred = new UsernameCredential (username);
        subject.getPublicCredentials().add (cred);
    }
}
```

### abort()

The `abort()` method is called when authentication doesn't succeed. Before the `abort()` method exits the `LoginModule`, care should be taken to reset state including the username and password input fields.

### logout()

The release of the users principals and credentials when `LoginContext.logout` is called:

```java
public boolean logout() {
    if (!subject.isReadOnly()) {
        Set principals = subject.getPrincipals(UserGroupPrincipal.class);
        subject.getPrincipals().removeAll(principals);
        Set creds = subject.getPublicCredentials(UsernameCredential.class);
        subject.getPublicCredentials().removeAll(creds);
        return true;
    } else {
        return false;
    }
}
```

## CallbackHandler.java

The `callbackHandler` is in a source (`.java`) file separate from any single `LoginModule` so that it can service a multitude of LoginModules with differing callback objects:

- Creates instance of the `CallbackHandler` class and has only one method, `handle()`.
- A `CallbackHandler` servicing a LoginModule requiring username & password to login:

```java
public void handle(Callback[] callbacks) {
    for (int i = 0; i < call