Using the default propagation token to propagate security attributes

A default propagation token is located on the running thread for applications and the security infrastructure to use. The product propagates this default propagation token downstream and the token stays on the thread where the invocation lands at each hop.

About this task

The data is available from within the container of any resource where the propagation token lands. Remember that you must enable the propagation feature at each server where a request is sent for propagation to work. Make sure that you enable security attribute propagation for all of the cells in your environment where you want propagation

There is a WSSecurityHelper class that has application programming interfaces (APIs) for accessing the PropagationToken attributes. This topic documents the usage scenarios and includes examples. A close relationship exists between the propagation token and the work area feature. The main difference between these features is that after you add attributes to the propagation token, you cannot change the attributes. You cannot change these attributes so that the security runtime can add auditable information and have that information remain there for the life of the invocation. Any time that you add an attribute to a specific key, an ArrayList object is stored to hold that attribute. Any new attribute that is added with the same key is added to the ArrayList object. When you call getAttributes, the ArrayList object is converted to a String array and the order is preserved. The first element in the String array is the first attribute added for that specific key.

In the default propagation token, a change flag is kept that logs any data changes to the token. These changes are tracked to enable WebSphere® Application Server to know when to send the authentication information downstream again so that the downstream server has those changes. Normally, Common Secure Interoperability Version 2 (CSIv2) maintains a session between servers for an authenticated client. If the propagation token changes, a new session is generated and subsequently a new authentication occurs. Frequent changes to the propagation token during a method cause frequent downstream calls. If you change the token prior to making many downstream calls or you change the token between each downstream call, you might impact security performance.

Procedure

Obtain the server list from the default propagation token.
Every time the propagation token is propagated and used to create the authenticated Subject, either horizontally or downstream, the name of the receiving application server is logged into the propagation token. The format of the host is "Cell:Node:Server", which provides you access to the cell name, node name, and server name of each application server that receives the invocation.
The following code provides you with this list of names and can be called from a Java™ 2 Platform, Enterprise Edition (J2EE) application.

The format of each server in the list is: cell:node_name:server_name. The output, for example, is: myManager:node1:server1
```
	String[] server_list = null;

	// If security is disabled on this application server, do not bother checking
	if (com.ibm.websphere.security.WSSecurityHelper.isServerSecurityEnabled())
	{
		try
		{
			// Gets the server_list string array
			server_list = com.ibm.websphere.security.WSSecurityHelper.getServerList();
		} 
		catch (Exception e)
		{
			// Performs normal exception handling for your application
		}

		if (server_list != null)
		{
			// print out each server in the list, server_list[0] is the first server
			for (int i=0; i<server_list.length; i++)
			{
				System.out.println("Server[" + i + "] = " + server_list[i]);
			}
		}
	}
```
Obtain the list of callers, using the getCallerList API.
A default propagation token is generated any time an authenticated user is set on the running thread or anyone tries to add attributes to the propagation token. Whenever an authenticated user is set on the thread, the user is logged in the default propagation token. At times, the same user might be logged in multiple times if the RunAs user is different from the caller. The following list provides the rules that are used to determine if a user that is added to the thread gets logged into the propagation token:
- The current Subject must be authenticated. For example, an unauthenticated Subject is not logged.
- The current authenticated Subject is logged if a Subject is not previously logged.
- The current authenticated Subject is logged if the last authenticated Subject that is logged does not contain the same user.
- The current authenticated Subject is logged on each unique application server that is involved in the propagation process.
The following code sample shows how to use the getCallerList API.

The format of each caller in the list is: cell:node_name:server_name:realm:port_number/securityName. The output, for example, is: myManager:node1:server1:ldap.austin.ibm.com:389/jsmith.
```
	String[] caller_list = null;

	// If security is disabled on this application server, do not check the caller list
	if (com.ibm.websphere.security.WSSecurityHelper.isServerSecurityEnabled())
	{
		try
		{
			// Gets the caller_list string array
			caller_list = com.ibm.websphere.security.WSSecurityHelper.getCallerList();
		} 
		catch (Exception e)
		{
			// Performs normal exception handling for your application
		}

		if (caller_list != null)
		{
			// Prints out each caller in the list, caller_list[0] is the first caller
			for (int i=0; i<caller_list.length;i++)
			{
				System.out.println("Caller[" + i + "] = " + caller_list[i]);
			}
		}
	}
```
Obtain the security name of the first authenticated user, using the getFirst Caller API.
Whenever you want to know which authenticated caller started the request, you can call the getFirstCaller method and the caller list is parsed. However, this method returns the security name of the caller only. If you need to know more than the security name, call the getCallerList method and retrieve the first entry in the String array. This entry provides all the caller information.
The following code sample retrieves the security name of the first authenticated caller using the getFirstCaller API.
The output, for example, is: jsmith.
```
	String first_caller = null;

	// If security is disabled on this application server, do not bother checking
	if (com.ibm.websphere.security.WSSecurityHelper.isServerSecurityEnabled())
	{
		try
		{
			// Gets the first caller
			first_caller = com.ibm.websphere.security.WSSecurityHelper.getFirstCaller();

			// Prints out the caller name
			System.out.println("First caller: " + first_caller);
		} 
		catch (Exception e)
		{
			// Performs normal exception handling for your application
		}
	}
```

Obtain the name of the first application server for a request, using the getFirstServer method.

Whenever you want to know what the first application server is for this request, call the getFirstServer method directly.

The following code sample retrieves the name of the first application server using the getFirstServer API.

The output, for example, is: myManager:node1:server1.

	String first_server = null;

	// If security is disabled on this application server, do not bother checking
	if (com.ibm.websphere.security.WSSecurityHelper.isServerSecurityEnabled())
	{
		try
		{
			// Gets the first server
			first_server = com.ibm.websphere.security.WSSecurityHelper.getFirstServer();

			// Prints out the server name
			System.out.println("First server: " + first_server);
		} 
		catch (Exception e)
		{
			// Performs normal exception handling for your application
		}
	}

Add custom attributes to the default propagation token, using the addPropagationAttribute API.
You can add custom attributes to the default propagation token for application usage. This token follows the request downstream so that the attributes are available when needed. When you use the default propagation token to add attributes, you must understand the following issues:
- Adding information to the propagation token affects CSIv2 session caching. Add information sparingly between remote requests.
- After you add information with a specific key, the information cannot be removed.
- You can add as many values to a specific key as you need. However, all of the values must be available from a returned String array in the order that they were added.
- The propagation token is available only on servers where propagation and security are enabled.
- The Java 2 Security javax.security.auth.AuthPermission wssecurity.addPropagationAttribute attribute is needed to add attributes to the default propagation token.
- An application cannot use keys that begin with either com.ibm.websphere.security or com.ibm.wsspi.security. These prefixes are reserved for system usage.
The following code sample shows how to use the addPropagationAttribute API.
```
	// If security is disabled on this application server, 
     // do not check the status of server security
	if (com.ibm.websphere.security.WSSecurityHelper.isServerSecurityEnabled())
	{
		try
		{
			// Specifies the key and values
			String key = "mykey";
			String value1 = "value1";
			String value2 = "value2";

			// Sets key, value1
       com.ibm.websphere.security.WSSecurityHelper.
       addPropagationAttribute (key, value1);

			// Sets key, value2
			String[] previous_values = com.ibm.websphere.security.WSSecurityHelper.
          addPropagationAttribute (key, value2);

			// Note: previous_values should contain value1
		} 
		catch (Exception e)
		{
			// Performs normal exception handling for your application
		}
	}
```
Obtain your custom attributes with the get PropagationAttributes API.
Custom attributes are added to the default propagation token using the addPropagationAttribute API. Retrieve these attributes using the getPropagationAttributes API. This token follows the request downstream so the attributes are available when needed. When you use the default propagation token to retrieve attributes, you must understand the following issues:
- The propagation token is available only on servers where propagation and security are enabled.
- The Java 2 Security javax.security.auth.AuthPermission "wssecurity.getPropagationAttributes" permission is needed to retrieve attributes from the default propagation token.
The following code sample shows how to use the getPropagationAttributes API.
```
	// If security is disabled on this application server, do not bother checking
	if (com.ibm.websphere.security.WSSecurityHelper.isServerSecurityEnabled())
	{
		try
		{
			String key = "mykey";
			String[] values = null;

			// Sets key, value1
       values = com.ibm.websphere.security.WSSecurityHelper.
       getPropagationAttributes (key);

			// Prints the values
			for (int i=0; i<values.length; i++)
			{
				System.out.println("Value[" + i + "] = " + values[i]);
			}
		} 
		catch (Exception e)
		{
			// Performs normal exception handling for your application
		}
	}
```
The output, for example, is:
Value[0] = value1
Value[1] = value2
Modify the propagation token factory configuration to use a token factory other than the default token factory.
When WebSphere Application Server generates a default propagation token, the Application Server utilizes the TokenFactory class that is specified using the com.ibm.wsspi.security.token.propagationTokenFactory property.

The default token factory that is specified for this property is called com.ibm.ws.security.ltpa.AuthzPropTokenFactory. This token factory encodes the data in the propagation token and does not encrypt the data. Because the propagation token typically flows over CSIv2 using Secure Sockets Layer (SSL), encrypting the token is not required. However, if you need additional security for the propagation token, you can associate a different token factory implementation with this property to get encryption. For example, if you choose to associate the com.ibm.ws.security.ltpa.LTPAToken2Factory token factory with this property, the token is AES encrypted. However, you need to weigh the performance impacts against your security needs. Adding sensitive information to the propagation token is a good reason to change the token factory implementation to something that encrypts rather than just encodes.
1. Open the administrative console.
2. Click Security > Global security.
3. Click Custom properties.
Perform your own signing and encryption of the default propagation token.
If you want to perform your own signing and encryption of the default propagation token, you must implement the following classes:
- com.ibm.wsspi.security.ltpa.Token
- com.ibm.wsspi.security.ltpa.TokenFactory
Your token factory implementation instantiates and validates your token implementation. You can choose to use the Lightweight Third Party Authentication (LTPA) keys and have them pass into the initialize method of the token factory, or you can use your own keys. If you use your own keys, they must be the same everywhere to validate the tokens that are generated using those keys. See the API documentation, available through a link on the front page of the documentation, for more information on implementing your own custom token factory.
Associate your token factory with the default propagation token.
1. Open the administrative console.
2. Click Security > Global security.
3. Click Custom properties.
4. Locate the com.ibm.wsspi.security.token.propagationTokenFactory property and verify that the value of this property matches your custom token factory implementation.
5. Verify that your implementation classes are put into the app_server_root/classes directory so that the WebSphere Application Server class loader can load the classes.
6. Verify that your implementation classes are located in the ${USER_INSTALL_ROOT}/classes directory so that the WebSphere Application Server class loader can load the classes.
7. Verify that the QEJBSVR user profile has read, write, and execute (*RWX) authority to the classes directory. You can use the Work with Authority (WRKAUT) command to view the authority permissions for the directory.