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Securing Servlets and JSPs in Sun Java System Application Server, Part 2

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Leonard Anghel concludes his series on security and the Sun Java System Application Server with a discussion of various security mechanisms, examples of the types of attacks you can expect, and suggestions on how to protect your websites against these malicious behaviors.
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Part 1 of this series showed you how to use declarative security in the Sun Java System Application Server (SJSAS) deployment descriptors to declare roles, users, groups, and realms. In this article, we'll consider how to implement some of the main website security approaches. We'll start with the authentication mechanisms and then discuss security annotations, programmatic security, and common attacks on JSP pages.

Types of Authentication

Now that we've provided a database for users/groups and passwords, it's time to see how to authenticate a user for our web application. We'll consider four types of authentication:

  • HTTP basic authentication
  • Digest authentication
  • Form-based authentication
  • HTTPS authentication

We'll look at each type of authentication based on the realms we defined earlier.

HTTP Basic Authentication

HTTP basic authentication is based on probably the most common and intuitive authentication scenario. When trying to connect to the server, the user has to provide a username and a password through a built-in interface. The server compares the client's credentials against a database of authorized users and accepts or rejects the user based on this comparison. Translating the authentication handshake into steps, we have the following:

  1. A client tries to access a protected resource.
  2. The server displays a built-in interface that requires the user credentials (username and password).
  3. The client types the credentials and submits them to the server. (The password is sent in Base64 encoding.)
  4. The server compares these credentials against a realm. If the authentication succeeds, the user is given access to the protected resource.

You can activate this kind of authentication from the web.xml descriptor as follows:

<login-config>
 <auth-method>BASIC</auth-method>
  <realm-name>MyFileRealm</realm-name>
</login-config>

Use those lines to replace the following comment in your web.xml file:

<!-- here we will paste the authentication mechanism -->

In this case, we've used the MyFileRealm realm developed in part 1 of this series. This realm contains two users:

  • TimmyTom can access the JSP files from the /jsps folder (JSP-ROLE role, JSP-USERS group).
  • MaryJane can access the SecureServlet servlet (SERVLET-ROLE role, SERVLET-USERS group).

No other user can access these resources.

Digest Authentication

Digest authentication is much like HTTP basic authentication. The difference between the two mechanisms occurs at transport level. With digest authentication, the password is encrypted before it's transmitted through wires; with basic authentication, the password is easily cracked because it's just encoded with a Base64 algorithm.

SJSAS doesn't implement digest authentication. In principle, the lines that should be added to web.xml for servers that support digest authentication (such as Tomcat) are as follows:

<login-config>
 <auth-method>DIGEST</auth-method>
  <realm-name>{the_realm}</realm-name>
</login-config>

Form-Based Authentication

Probably the most frequently used authentication mechanism is form-based authentication. This kind of authentication improves on basic authentication by adding the capability of controlling the look and feel of the login interface. In addition, a rejected user is redirected to a custom error page, rather than simply receiving a "forbidden" error message. The steps of form-based authentication are as follows:

  1. A client tries to access a protected resource.
  2. The server redirects the user request to a custom interface that requires the user credentials (username and password). We named this interface login.jsp (see Figure 1).
  3. The client types the credentials and submits them to the server (via unsecured transport).
  4. The server compares these credentials against a realm. If the authentication succeeds, the user is given access to the protected resource. If authentication fails, the client is forwarded or redirected to a custom error page. We named the error page loginError.jsp.

You can activate this kind of authentication from the web.xml descriptor as follows:

<login-config>
 <auth-method>FORM</auth-method>
 <realm-name>MyJDBCRealm</realm-name>
 <form-login-config>
  <form-login-page>/jaas_login/login.jsp</form-login-page>
  <form-error-page>/jaas_login/loginError.jsp</form-error-page>
 </form-login-config>
</login-config>

Use those lines to replace the following comment in your web.xml file:

<!-- here we will paste the authentication mechanism -->

The login.jsp page code may look as follows:

<!-- j_security_check - the login form's action -->
<form method="POST" action="j_security_check">
 <table align="center" width="100">
  <tr bgcolor="#000000">
    <td>
     <font size="1" face="Arial" color="#ffffff">
      <strong>User:</strong>
     </font>
    </td>
    <td>
     <!-- j_username - the name of the username field -->
     <input type="text" name="j_username" />
    </td>
  </tr>
  <tr bgcolor="#000000">
    <td>
     <font size="1" face="Arial" color="#ffffff">
      <strong>Password:</strong>
     </font>
    </td>
    <td>
     <!-- j_password - the name of the password field -->
     <input type="password" name="j_password" />
    </td>
   </tr>
   <tr bgcolor="#000000">
    <td>
     <input type="submit" value="Login" />
    </td>
   </tr>
  </table>
 </form>
...

loginError.jsp doesn't contain any mandatory parts; therefore, you're free to use your imagination and develop the error page as you like.

In this case, we've used the MyJDBCRealm realm developed in part 1 of this series. This realm contains two users:

  • ShawnRay can access the JSP files from the /jsps folder (JSP-ROLE role, JSP-USERS group).
  • MarchusRuhl can access the SecureServlet servlet (SERVLET-ROLE role, SERVLET-USERS group).

No other user can access these resources.

HTTPS Authentication

HTTPS authentication is based on the SSL transport mechanism. This transport guarantees an encrypted communication between server and client, meant to ensure privacy for the transmitted data. Before any private data is transmitted, however, the server presents to the web browser a set of credentials in the form of a server certificate. (This procedure, known as the SSL handshake, must be completed before the HTTP request is accessed.)

In addition, the server may require that the client present in exchange a client certificate (in this case, we're talking about mutual authentication over SSL). The server certificate proves to the client that the site is who it claims to be, and the client certificate proves to the server that the client or user is who it claims to be.

In SJSAS, SSL support is enabled and ready to be used (by default, the SSL-HTTPS connector is activated and can be tested on https://localhost:8181/). For other servers, check the server documentation to see how to activate the SSL-HTTPS connector (if it isn't already activated).

Before specifying a secure connection, you should know that SSL is commonly used when the login authentication method is set to BASIC or FORM. Since these two authentication mechanisms are based on unsecured transport, it's a good idea to enforce them with the SSL transport support. The transport type is indicated in the web.xml descriptor through the <transport-guarantee> element. The values supported by this element are shown in the following table.

Value Description
NONE Unsecured transport.
INTEGRAL The data cannot be changed in transit between client and server.
CONFIDENTIAL The changed content is invisible to anyone/anything from outside the process.

Next, we set the CONFIDENTIAL security level for the SecureServlet resource:

<security-constraint>
 <web-resource-collection>
   <web-resource-name>Secure Servlet</web-resource-name>
   <url-pattern>/SecureServlet</url-pattern>
   <http-method>GET</http-method>
   <http-method>POST</http-method>
 </web-resource-collection>
   <auth-constraint>
     <role-name>SERVLET-ROLE</role-name>
   </auth-constraint>
   <user-data-constraint>
     <transport-guarantee>CONFIDENTIAL</transport-guarantee>
   </user-data-constraint>
</security-constraint>

Notice that the server proves its identity by showing the client the server's auto-signed certificate from mykeystore.jks. (We created this certificate in part 1, customizing the SJSAS configuration to point to our keystore and truststore instead of the defaults.) Depending on the browser, an attention message may be triggered, indicating that the certificate is self-signed and asking the user to accept it as a trust certificate. Once the certificate has been accepted, the user will not be prompted to accept the certificate again at the next connection.

Mutual Authentication Over SSL

When the server is proving its identity through security certificates, it's quite fair to ask the client to prove its identity as well. When a server provides identification as well as requiring client authentication, the authentication is called mutual authentication or two-way authentication.

Mutual authentication can be activated from web.xml by specifying the CLIENT-CERT value for the authentication method (<auth-method> element). For example, if we want to rewrite web.xml to use mutual authentication for protecting the /jsps folder and the SecureServlet through the SERVLET-CERT-ROLE role, we can do it as shown in Listing 1.

Listing 1 web.xml.

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee

 <display-name>Roles</display-name>

 <servlet>
  <servlet-name>SecureServlet</servlet-name>
  <servlet-class>secure.servlet.SecureServlet</servlet-class>
  <security-role-ref>
        <role-name>SERVLET-ROLE-ALIAS</role-name>
        <role-link>SERVLET-CERT-ROLE</role-link>
  </security-role-ref>
 </servlet>
 <servlet-mapping>
  <servlet-name>SecureServlet</servlet-name>
  <url-pattern>/SecureServlet</url-pattern>
 </servlet-mapping>

  <security-role>
   <role-name>SERVLET-CERT-ROLE</role-name>
 </security-role>

 <security-constraint>
    <web-resource-collection>
      <web-resource-name>Secure Servlet</web-resource-name>
      <url-pattern>/SecureServlet</url-pattern>
      <http-method>GET</http-method>
      <http-method>POST</http-method>
    </web-resource-collection>
    <auth-constraint>
      <role-name>SERVLET-CERT-ROLE</role-name>
    </auth-constraint>
    <user-data-constraint>
     <transport-guarantee>CONFIDENTIAL</transport-guarantee>
    </user-data-constraint>
 </security-constraint>

  <security-constraint>
    <web-resource-collection>
      <web-resource-name>Secure JSPs</web-resource-name>
      <url-pattern>/jsps/*</url-pattern>
      <http-method>GET</http-method>
      <http-method>POST</http-method>
    </web-resource-collection>
    <auth-constraint>
      <role-name>SERVLET-CERT-ROLE</role-name>
    </auth-constraint>
    <user-data-constraint>
     <transport-guarantee>CONFIDENTIAL</transport-guarantee>
   </user-data-constraint>
  </security-constraint>

 <login-config>
  <auth-method>CLIENT-CERT</auth-method>
  <realm-name>MyCertificateRealm</realm-name>
 </login-config>

 <welcome-file-list>
  <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>

</web-app>

The SERVLET-CERT-ROLE should be mapped to a principal in sun-application.xml or sun-web.xml as follows:

<security-role-mapping>
    <role-name>SERVLET-CERT-ROLE</role-name>
    <principal-name>CN=Mike, OU=home.user, C=RO</principal-name>
    <group-name>SERVLET-CERT-USERS</group-name>
</security-role-mapping>

The <principal-name> value must correspond to the client certificate entries:

  • CN answers the question, "What is your first and last name?"
  • OU answers the question, "What is the name of your organization unit?"
  • C answers the question, "What is the two-letter country code for this unit?"

After you obtain a certificate from a certificate authority, you have to make SJSAS aware of the certificate's location, and you have to import the certificate into your browser. Mozilla.org provides details on importing certificates in Mozilla, and Microsoft provides comparable information on using digital certificates with Internet Explorer.

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