When you develop Session Initiation Protocol (SIP) applications,
you can create a custom trust association interceptor (TAI).
Before you begin
You may want to
familiarize yourself with the general TAI information contained in the Trust Associations documentation.
Developing a SIP TAI is similar to developing any other custom interceptors
used in trust associations. In fact, a custom TAI for a SIP application is
actually an extension of the trust association interceptor model. Refer to
the Developing a custom
interceptor for trust associations section for more details.
About this task
TAI can be invoked by a SIP servlet request or a SIP servlet response.
To implement a custom SIP TAI, you need to write your own Java class.
Procedure
- Write a Java class that extends the com.ibm.wsspi.security.tai.BaseTrustAssociationInterceptor class
and implements the com.ibm.websphere.security.tai.SIPTrustAssociationInterceptor interface.
Those classes are defined in the WASProductDir/plugins/com.ibm.ws.sip.container_1.0.0.jar file,
where WASProductDir is the fully qualified path name of
the directory in which WebSphere Application Server is installed.
- Declare the following Java methods:
- public int initialize(Properties properties) throws WebTrustAssociationFailedException;
- This is invoked before the first message is processed so that the implementation
can allocate any resources it needs. For example, it could establish a connection
to a database. WebTrustAssociationFailedException is defined
in the WASProductDir/plugins/com.ibm.ws.runtime_1.0.0.jar file.
The value of the properties argument comes from the Custom
Properties set in this
step.
- public void cleanup();
- This is invoked when the TAI should free any resources it holds. For example,
it could close a connection to a database.
- public boolean isTargetProtocolInterceptor(SipServletMessage sipMsg)
throws WebTrustAssociationFailedException;
- Your custom TAI should use this method to handle the sipMsg message.
If the method returns false, WebSphere ignores your TAI for sipMsg.
- public TAIResult negotiateValidateandEstablishProtocolTrust (SipServletRequest
req, SipServletResponse resp) throws WebTrustAssociationFailedException;
- This method returns a TAIResult that indicates the status of the message
being processed and a user ID or the unique ID for the user who is trying
to authenticate. If authentication succeeds, the TAIResult should contain
the status HttpServletResponse.SC_OK and a principal. If authentication fails,
the TAIResult should contain a return code of HttpServletResponse.SC_UNAUTHORIZED
(401), SC_FORBIDDEN (403), or SC_PROXY_AUTHENTICATION_REQUIRED (407). This
only indicates whether or not the container should accept a message for further
processing. To challenge an incoming request, the TAI implementation must
generate and send its own SipServletResponse containing a challenge. The exception
should be thrown for internal TAI errors. Description of negotiateValidateandEstablishProtocolTrust arguments and actions describes
the argument values and resultant actions for the negotiateValidateandEstablishProtocolTrust
method.
Table 1. Description of negotiateValidateandEstablishProtocolTrust
arguments and actions
Argument or action |
For a SIP request |
For a SIP response |
Value of req argument |
The incoming request |
Null |
Value of resp argument |
Null |
The incoming response |
Action for valid response credentials |
Return TAIResult.status containing SC_OK and a user
ID or unique ID |
Return TAIResult.status containing SC_OK and a user
ID or unique ID |
Action for incorrect response credentials |
Return the TAIResult with the 4xx status |
Return the TAIResult with the 4xx status |
The sequence of events is as follows:
- The SIP container maps initial requests to applications by using the rules
in each applications deployment descriptor; subsequent messages are mapped
based on JSR 116 mechanisms.
- If any of the applications require security, the SIP container invokes
any defined TAI implementations for the message.
- If the message passes security, the container invokes the corresponding
applications.
Your TAI implementation can modify a SIP message, but the modified message
will not be usable within the request mapping process, because it finishes
before the container invokes the TAI.The com.ibm.wsspi.security.tai.TAIResult
class, defined in the WASProductDir/plugins/com.ibm.ws.runtime_1.0.0.jar file,
has three static methods for creating a TAIResult. The TAIResult create methods
take an int type as the first parameter. WebSphere Application Server expects
the result to be a valid HTTP request return code and is interpreted as follows:
If
the value is HttpServletResponse.SC_OK, this response tells WebSphere Application
Server that the TAI has completed its negotiation. The response also tells
WebSphere Application Server use the information in the TAIResult to create
a user identity.
The created TAIResults have the meanings shown in Meanings of TAIResults.
Table 2. Meanings of TAIResults
TAIResult |
Explanation |
public static TAIResult create(int status); |
Indicates a status to WebSphere Application Server.
The status should not be SC_OK because the identity information is provided. |
public static TAIResult create(int status, String principal); |
Indicates a status to WebSphere Application Server and
provides the user ID or the unique ID for this user. WebSphere Application
Server creates credentials by querying the user registry. |
public static TAIResult create(int status, String principal,
Subject subject); |
Indicates a status to WebSphere Application Server,
the user ID or the unique ID for the user, and a custom Subject. If the Subject
contains a Hashtable, the principal is ignored. The contents of the Subject
becomes part of the eventual user Subject. |
- public String getVersion();
- This method returns the version number of the current TAI implementation.
- public String getType();
- This method's return value is implementation-dependent.
- Compile the implementation after you have implemented it. For example: /opt/WebSphere/AppServer/java/bin/javac
-classpath /opt/WebSphere/AppServer/plugins/com.ibm.ws.runtime_1.0.0.jar;/opt/WebSphere/AppServer/lib/j2ee.jar;/opt/WebSphere/AppServer/plugins/com.ibm.ws.sip.container_1.0.0.jar
myTAIImpl.java
- For each server within a cluster, copy the class file to a location
in the WebSphere class path (preferably the WASProductDir/plugin/ directory).
- Restart all the servers.
- Delete the default WebSEAL interceptor in the administrative console
and click New to add your custom interceptor. Verify
that the class name is dot-separated and appears in the class path.
- Click the Custom Properties link
to add additional properties that are required to initialize the custom interceptor.
These properties are passed to the initialize(Properties properties) method
of your implementation when it extends the com.ibm.websphere.security.WebSphereBaseTrustAssociationInterceptor as
described in the previous step.
- Save and synchronize (if applicable) the configuration.
- Restart the servers for the custom interceptor to take effect.