WebSphere Application Server provides a trust association
interceptor (TAI) that uses the Simple and Protected GSS-API Negotiation
Mechanism (SPNEGO) to securely negotiate and authenticate HTTP requests
for secured resources in WebSphere Application Server.
SPNEGO is a standard specification defined in The Simple and Protected GSS-API Negotiation Mechanism
(IETF RFC 2478).
When WebSphere Application Server administrative security is enabled,
the SPNEGO TAI is initialized. While processing inbound HTTP requests,
the Web authenticator component interacts with the SPNEGO TAI, which
is defined and enabled in the security configuration repository. One
interceptor is selected and is responsible for authenticating access
to the secured resource that is identified in the HTTP request.
Important: The use of TAIs is an optional feature. If no TAI
is selected, the authentication process continues normally.
HTTP users log in and authenticate only once at their desktop and
are subsequently authenticated (internally) with WebSphere Application
Server. The SPNEGO TAI is invisible to the end-user of WebSphere applications.
The SPNEGO TAI is only visible to the Web administrator who is responsible
for ensuring a proper configuration, capacity, and maintenance of
the Web environment.
In addition to WebSphere Application Server security runtime services,
some external components are required to completely enable operation
of the SPNEGO TAI. The external components include:
Microsoft Windows Servers with
Active Directory domain and associated Kerberos Key Distribution Center
(KDC). For information on the supported Microsoft Windows Servers,
see the System Requirements for WebSphere Application Server Version 6.1 on Windows.
- A client application, for example, a browser or Microsoft .NET
client, that supports the SPNEGO authentication mechanism, as defined
in IETF RFC 2478. Microsoft Internet Explorer Version 5.5 or later
and Mozilla Firefox Version 1.0 are browser examples. Any browser
needs to be configured to use the SPNEGO mechanism. For more information
on performing this configuration, see Configuring the client browser to use SPNEGO.
The authentication of HTTP requests is triggered by the requestor
(the client-side), which generates a SPNEGO token. WebSphere Application
Server receives this token and validates trust between the requester
and WebSphere Application Server. Specifically, the SPNEGO TAI decodes
and retrieves the requester's identity from the SPNEGO token. The
identity is used to establish a secure context between the requester
and the application server.
Remember: The SPNEGO TAI is
a server-side solution in WebSphere Application Server. Client-side
applications are responsible for generating the SPNEGO token for use
by the SPNEGO TAI. The requester's identity in WebSphere Application
Server security registry must be identical to that identity the SPNEGO
TAI retrieves. An identical match does occur when Microsoft Windows
Active Directory server is the Lightweight Directory Access Protocol
(LDAP) server that is used in WebSphere Application Server. A custom
login module is available as a plug-in to support custom mapping of
the identity from the Active Directory to the WebSphere Application
Server security registry. See
Mapping Kerberos client principal name to WebSphere user registry ID for SPNEGO for details on using this custom login module.
WebSphere Application Server validates the identity against its security
registry and, if the validation is successful, produces a Lightweight
Third Party Authentication (LTPA) security token and places and returns
a cookie to the requester in the HTTP response. Subsequent HTTP requests
from this same requester to access additional secured resources in
WebSphere Application Server use the LTPA security token previously
created, to avoid repeated login challenges.
The challenge-response handshake process is illustrated in the
following graphic:
Figure 1. HTTP request processing, WebSphere Application Server
- SPNEGO TAI
The SPNEGO TAI can be enabled for all or for selected WebSphere
Application Servers in a WebSphere Application Server cell configuration.
Also, the behavior of each SPNEGO TAI instance is controlled by custom
configuration properties that are used to identify, for example, the
criteria used to filter HTTP requests, such as the host name and security
realm name used to construct the Kerberos Service Principal Name (SPN).
For more information regarding establishing and setting the SPNEGO
TAI custom configuration properties, see the following topics:
The Web administrator has access to the following SPNEGO TAI security
components and associated configuration data, as illustrated in the
following graphic.
Figure 2. SPNEGO TAI security and configuration elements

- The Web authentication module and the Lightweight Third Party
Authentication (LTPA) mechanism provide the plug-in runtime framework
for trust association interceptors. See Configuring the Lightweight Third Party Authentication mechanism for more detail is configuring the LTPA mechanism
for use with the SPNEGO TAI.
- The Java Generic Security Service (JGSS) provider is included
in the Java SDK (jre/lib/ibmjgssprovider.jarapp_server_root/java/endorsed/ibmjgssprovider.jar) and used to obtain the Kerberos security context and credentials
that are used for authentication. IBM JGSS 1.0 is a Java Generic Security
Service Application Programming Interface (GSSAPI) framework with
Kerberos V5 as the underlying default security mechanism. GSSAPI is
a standardized abstract interface under which can be plugged different
security mechanisms based on private-key, public-key and other security
technologies. GSSAPI shields secure applications from the complexities
and peculiarities of the different underlying security mechanisms.
GSSAPI provides identity and message origin authentication, message
integrity, and message confidentiality. For more information, see JGSS.
- The Kerberos configuration properties (krb5.conf or krb5.ini ) and Kerberos encryption keys (stored
in a Kerberos keytab file) are used to establish secure mutual authentication.
The Kerberos key table manager (Ktab), which is part of JGSS, allows
you to manage the principal names and service keys stored in a local
Kerberos keytab file. Principal name and key pairs listed in the Kerberos
keytab file allow services running on a host to authenticate themselves
to the Kerberos Key Distribution Center (KDC). Before a server can
use Kerberos, a Kerberos keytab file must be initialized on the host
that runs the server.
Using the ktutil command to manage the Kerberos keytab file highlights the Kerberos configuration requirements
for the SPNEGO TAI as well as the use of Ktab.
- The SPNEGO provider supplies the implementation of the SPNEGO
authentication mechanism, located at /$WAS_HOME/java/jre/lib/ext/ibmspnego.jarapp_server_root/java/ext/ibmspnego.jar.
- The custom configuration properties control the runtime behavior
of the SPNEGO TAI. Configuration operations are performed with the
administrative console or scripting facilities. Refer to SPNEGO TAI custom properties configuration for more
information about these custom configuration properties.
- Java virtual machine (JVM) custom properties control diagnostic
trace information for problem determination of the JGSS security provider
and use of the property reload feature.SPNEGO TAI JVM configuration custom properties describes
these JVM custom properties
The benefits of having WebSphere Application Server use the SPNEGO
TAI include:
An integrated single signon environment
with Microsoft Windows Servers using Active Directory domain is established.
- The cost of administering a large number of ids and passwords
is reduced.
- A secure and mutually authenticated transmission of security credentials
from the Web browser or Microsoft .NET clients is established.
- Interoperability with Web services and Microsoft .NET applications
that use SPNEGO authentication at the transport level is achieved.
Using the SPNEGO TAI in your WebSphere Application Server environment
requires planning then implementation. See
Single sign-on capability with SPNEGO TAI - checklist in
planning for SPNEGO TAI. Implementing the use of the SPNEGO TAI is
divided into the following areas of responsibility:
- End browser user
- The end user must configure the Web browser or Microsoft .NET
application to issue HTTP requests that are processed by the SPNEGO
TAI.
- Web administrator
- The Web administrator is responsible for configuring the SPNEGO
TAI of WebSphere Application Server to respond to HTTP requests of
the client.
- WebSphere Application Server administrator
- The WebSphere Application Server administrator is responsible
for configuring WebSphere Application Server and the SPNEGO TAI for
optimum installation performance.
See
Creating a single sign-on for HTTP requests using the SPNEGO TAI for an explanation of the tasks required to use the SPNEGO TAI and
how the responsible party performs these tasks.