Welcome!

Java IoT Authors: Elizabeth White, Liz McMillan, Pat Romanski, Stackify Blog, Progress Blog

Related Topics: Open Source Cloud, Java IoT, Microservices Expo, Apache

Open Source Cloud: Article

Valve, JAAS and Filter in Tomcat

Their usages and relationships

Tomcat is a widely popular lightweight application server. When securing Tomcat web applications, Valve, JAAS and Filter are used in various scenarios. The challenges for developers are when to use each of these methods and how to integrate them together if more than one method is chosen. For example, the WebSeal agent discussed in the article [1] uses Valve. If a customer needs to integrate WebSeal and its own JAAS-based authentication module, they will need to know how to configure Tomcat to use both the WebSeal Agent Valve and the JAAS module and how to pass information between them.

In this article, we will explain the concepts of Valve, JAAS and Filter, and their relationships such as the order that they get called. Through an example application, we will explain how you can use them together and pass information among them for an authentication process. How to configure and run the example application using Tomcat 7 will also be discussed.

The Concepts
Valve

A Valve is a piece of Java code that can be inserted into the request processing pipeline. The Valve can be defined on a different scope such as Engine, Host and Context. Tomcat comes with a set of pre-built valves that can be found here [2]. However, developers can write their own Valve and participate in the processing of the Valve chain. The main requirements for a Valve are:

  • It needs to extend ValveBase
  • It needs to call getNext().invoke(request, response) to chain other Valves.

For example, Listing 1 is a simple Valve. (Listings 1 - 5 can be downloaded here.) That Valve also has a method that may call an external policy server to verify the user. It may retrieve the user information passed in as a token in the HTTP header field such as the one used in [1]. You can ignore the ThreadLocale part in the Listing 1, which will be discussed later.

JAAS
Java Authentication and Authorization Service (JAAS) [3] is a security framework that allows a user's program to participate in the authentication and authorization process. JAAS also serves as an integration point to allow different user-specific security implementations to be used. JAAS is supported in Tomcat through its JAASRealm interface [4].

When JAASRealm is used, a user will need to provide a login module and the appropriate configurations: a configuration file and a security configuration in the web.xml. Once it's configured properly, the login module will be called and managed by the Tomcat.

Listing 2 has a sample JAAS login module. This login module will use a callback to get the userid and password. It will check whether the password is the reverse of the userid. If the check succeeds, it will create a principal based on the username and assign the role "jvalve" to the principal.

Filter
A filter is part of the Java Servlet specification [5]. A filter can be inserted into the request processing pipeline. It will be executed before the servlet is called and invoked again when the servlet process is done. Multiple filters can be chained together and thus can be used as an integration point for different users who want to use the filter to accomplish certain cross-cutting functions. The main requirements for a filter are:

  • It needs to extend javax.servlet.Filter.
  • It needs to call chain.doFilter(request, response).

Listing 3 shows an example filter. This filter simply calculates the time used to complete the request.

The Relationships
All three technologies, Valve, JAAS and Filter, have the following commonalities:

  • Run before the servlet is invoked
  • Allow cross-cutting functions to be implemented.
  • Provide integration points to allow multiple Valves, login modules and filters to be defined by different users.
  • Provide a common place for implementing security features.

Even though JAAS is the official method for providing security implementations, Valve and filter have been used to implement securities frequently. Especially in the Tomcat case, it is relatively hard to get a Subject in the application code (JBoss has a SharedState, WebLogic and WebSphere all provide a static method to make the "Subject" available for the application code). Implementations may use Valve for the authentication and then set the authenticated principal on the request for the filter and application code to use.

However, it's also important to understand their differences especially if you want to use them together.

  • The order that they get invoked is as follows: Valve, JAAS module, Filter and then Servlet.
  • Valve and Filter have access to a request/response/session, etc. However, JAAS only has access to the shared state. It can interact with the Tomcat container to retrieve such things as security information, but can only do so through callbacks.

Because of the above differences, it becomes a challenge if you want to use all three of them together and pass information among them. Consider the following example. Tivilo WebSeal provides a Valve engine that will set an authenticated user on the request. Your company has been using the JAAS module for the additional authentication purpose. The JAAS module will want to retrieve that authenticated user from the Valve. Tomcat will not help in this case. In the next session, we'll discuss a ThreadLocale [6] solution to address this issue.

The Sample Application
The sample application uses the Valve, the JAAS login module and the filter in Listings 1, 2, and 3. However, we want to retrieve a key in the Valve and pass it to the JAAS login module. We will use the ThreadLocale to accomplish this. Listing 4 shows the ThreadLocale class.

In Listing 1, we have set the "key" to the ThreadLocale. In Listing 2 of the JAAS code, we have code to retrieve the "key" from the ThreadLocale (it is commented out). We define the value of the password as the reverse of the username plus the key (it's commented out in Listing 2 as well).

The web.xml, which protects the secured resource and defines the filter, is listed in Listing 5.

The JAAS login module can be defined in the following login.config file:

MyAccess {
com.sas.tcserver.SampleLoginModule required
debug=true;
};

This same ThreadLocale concept can be used if a user wants to pass information from the JAAS login module to the filter.

Issues with Tomcat 6
If you are using Tomcat 6 and plan to create a user principal at the Valve, the JAAS login module will not be called by Tomcat.

For example, you have the following code in your Valve's "invoke()" method:

GenericPrincipal genericprincipal = new
GenericPrincipal(request.getContext().getRealm(), "user", null,
arraylist
, null);
request.setUserPrincipal(genericprincipal);

This problem does not occur at Tomcat 7. It should note that the construct for GenericPrincipal has been changed from 6 to 7. In Tomcat 7, you will do:

GenericPrincipal genericprincipal = new
GenericPrincipal("user", null, arraylist, null);
request.setUserPrincipal(genericprincipal);

Configure and Run the Sample Application
The sample application is packaged into the following files: 1) A src folder, which contains all source code; 2) securityvalve.jar; 3) loginmodule war file, which includes the sampleloginmodule.jar and timerfilter.jar. The files can be downloaded from here.

To run the application, complete the following process:

  • Download and install Tomcat 7.
  • Unzip the downloaded file.
  • Copy securityvalve.jar into Tomcat lib directory
  • Copy loginmodule war (in exploded format) into Tomcat webapps directory
  • Add the following xml piece into Tomcat conf/server.xml file inside Services -> Engine -> Host:

<Context path="/loginmodule">
<Realm
className="org.apache.catalina.realm.JAASRealm           
appName="MyAccess"          
userClassNames="com.sas.tcserver.SampleUserPrincipal"        
roleClassNames="com.sas.tcserver.SampleRolePrincipal"/>

<Valve className="com.sas.tcserver.SecurityValve"
debugTrace="true"/>
</Context>

  • Create login.config file in Tomcat conf directory using the content in the previous section.
  • Update Tomcat startup command to add the following parameter:

-Djava.security.auth.login.config=%CATALINA_BASE%\conf\login.config

  • Start Tomcat
  • Access the application in Web browser using the following URL: http://localhost:8080/loginmodule/index.html. When prompted, type in "jvalve/velavjsas" as username/password, you should see the following output in the Tomcat console:

Security Valve: invoke
SampleLoginModule: initialize
SampleLoginModule - initialize - subject: Subject:

SampleLoginModule - initialize - sharedState: {}
SampleLoginModule: login
SampleUserPrincipal
SampleLoginModule: commit
SampleRolePrincipal
SampleLoginModule: commit successful
TimerFilter: Time to execute request: 2 milliseconds
Security Valve: exit invoke

In the above output, you may notice that the Valve works like filters but is called before and after JAAS and the filters. We use the password "velavjsas", which is the reverse of username "jvalve" plus the key that is passed from the Valve to the JAAS module using the ThreadLocale.

Conclusion
Valve, JAAS and Filter are common technologies in Tomcat. However, to configure and use them together requires a basic understanding of their relationships. This article explained the concepts and demonstrated their usages and relationships through a sample application. The sample application can be easily expanded and used in various authentication processes.

The concept discussed here can also be used in other Tomcat based application servers such as the VMware vFabric tc Server [7].

Resources

  1. How do I integrate SSO on Apache Tomcat
  2. Apache Tomcat 7: The Valve Component
  3. All that JAAS
  4. Tomcat Class JAASRealm
  5. The Essentials of Filters
  6. ThreadLocale
  7. VMware vFabric tc Server

More Stories By Zhiyong Li

Zhiyong Li is a senior manager of SAS Platform Division and the chair of the Java Technology Board at SAS institute. He started coding in Java in 1995 as a Sun’s development staff. He worked at IBM and iBiomatics as lead architect and developer for several enterprises Java applications. He holds a Ph.D from Computer Science Department of Duke University. He has published many papers in AI, parallel computation and program languages. He has also published several patents.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
SYS-CON Events announced today that DXWorldExpo has been named “Global Sponsor” of SYS-CON's 21st International Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Digital Transformation is the key issue driving the global enterprise IT business. Digital Transformation is most prominent among Global 2000 enterprises and government institutions.
SYS-CON Events announced today that Nihon Micron will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Nihon Micron Co., Ltd. strives for technological innovation to establish high-density, high-precision processing technology for providing printed circuit board and metal mount RFID tags used for communication devices. For more inf...
SYS-CON Events announced today that Ryobi Systems will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ryobi Systems Co., Ltd., as an information service company, specialized in business support for local governments and medical industry. We are challenging to achive the precision farming with AI. For more information, visit http:...
SYS-CON Events announced today that mruby Forum will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. mruby is the lightweight implementation of the Ruby language. We introduce mruby and the mruby IoT framework that enhances development productivity. For more information, visit http://forum.mruby.org/.
SYS-CON Events announced today that Mobile Create USA will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Mobile Create USA Inc. is an MVNO-based business model that uses portable communication devices and cellular-based infrastructure in the development, sales, operation and mobile communications systems incorporating GPS capabi...
SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
SYS-CON Events announced today that Daiya Industry will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Daiya Industry specializes in orthotic support systems and assistive devices with pneumatic artificial muscles in order to contribute to an extended healthy life expectancy. For more information, please visit https://www.daiyak...
SYS-CON Events announced today that Fusic will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Fusic Co. provides mocks as virtual IoT devices. You can customize mocks, and get any amount of data at any time in your test. For more information, visit https://fusic.co.jp/english/.
SYS-CON Events announced today that Keisoku Research Consultant Co. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Keisoku Research Consultant, Co. offers research and consulting in a wide range of civil engineering-related fields from information construction to preservation of cultural properties. For more information, vi...
SYS-CON Events announced today that Interface Corporation will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Interface Corporation is a company developing, manufacturing and marketing high quality and wide variety of industrial computers and interface modules such as PCIs and PCI express. For more information, visit http://www.i...
Elon Musk is among the notable industry figures who worries about the power of AI to destroy rather than help society. Mark Zuckerberg, on the other hand, embraces all that is going on. AI is most powerful when deployed across the vast networks being built for Internets of Things in the manufacturing, transportation and logistics, retail, healthcare, government and other sectors. Is AI transforming IoT for the good or the bad? Do we need to worry about its potential destructive power? Or will we...
SYS-CON Events announced today that Enroute Lab will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Enroute Lab is an industrial design, research and development company of unmanned robotic vehicle system. For more information, please visit http://elab.co.jp/.
In his session at @ThingsExpo, Greg Gorman is the Director, IoT Developer Ecosystem, Watson IoT, will provide a short tutorial on Node-RED, a Node.js-based programming tool for wiring together hardware devices, APIs and online services in new and interesting ways. It provides a browser-based editor that makes it easy to wire together flows using a wide range of nodes in the palette that can be deployed to its runtime in a single-click. There is a large library of contributed nodes that help so...
DevOps at Cloud Expo – being held October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real r...
While some developers care passionately about how data centers and clouds are architected, for most, it is only the end result that matters. To the majority of companies, technology exists to solve a business problem, and only delivers value when it is solving that problem. 2017 brings the mainstream adoption of containers for production workloads. In his session at 21st Cloud Expo, Ben McCormack, VP of Operations at Evernote, will discuss how data centers of the future will be managed, how th...
SYS-CON Events announced today that Massive Networks, that helps your business operate seamlessly with fast, reliable, and secure internet and network solutions, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. As a premier telecommunications provider, Massive Networks is headquartered out of Louisville, Colorado. With years of experience under their belt, their team of...
SYS-CON Events announced today that TMC has been named “Media Sponsor” of SYS-CON's 21st International Cloud Expo and Big Data at Cloud Expo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Global buyers rely on TMC’s content-driven marketplaces to make purchase decisions and navigate markets. Learn how we can help you reach your marketing goals.
There is huge complexity in implementing a successful digital business that requires efficient on-premise and cloud back-end infrastructure, IT and Internet of Things (IoT) data, analytics, Machine Learning, Artificial Intelligence (AI) and Digital Applications. In the data center alone, there are physical and virtual infrastructures, multiple operating systems, multiple applications and new and emerging business and technological paradigms such as cloud computing and XaaS. And then there are pe...
Real IoT production deployments running at scale are collecting sensor data from hundreds / thousands / millions of devices. The goal is to take business-critical actions on the real-time data and find insights from stored datasets. In his session at @ThingsExpo, John Walicki, Watson IoT Developer Advocate at IBM Cloud, will provide a fast-paced developer journey that follows the IoT sensor data from generation, to edge gateway, to edge analytics, to encryption, to the IBM Bluemix cloud, to Wa...
With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend 21st Cloud Expo October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.