Jars can't be signed with different certificates---even by Sun?

Question

I am deploying an application which uses the following jar files:
com.example.application.jar
com.example.support.jar
javax.activation.jar
javax.mail.jar
The latter two are jars signed from Sun, yet JWS complains that the jars have been signed with different certificates. I'm forced to unpack the Sun jars and repackage them,signing them with my own certificate.
Isn't this a little restrictive? Shouldn't jars signed by Sun be exceptions to the "all jars signed by the same certificate" requirement?
Garret

Answer 1

Thanks! The JNLP 1.5 MR specification is a bit opaque about exactly how to do this, but the following site has an example that helped:
http://java.sun.com/j2se/1.5.0/docs/guide/javaws/developersguide/faq.html
The example didn't mention whether I can request all permissions for the component extension, but I suppose I can. Nothing seems to indicate whether I can have component extensions reference other component extensions (JavaMail requires JAF, for example), but it seems to work.
By requesting full permissions for the component extensions, though, I now get two dialogs presented to the user, the first asking if my application should be trusted, and the second asking if Sun Microsystems should be trusted.
If I remove all-permissions from the JavaMail component extension, yet request it for the main application (thereby only presenting the user with one confirmation dialog), will I still be able to perform restricted functionality using JavaMail, such as connecting to remote servers?
Here's what I'm now using, in hopes that it benefits someone else. The main JNLP:
     <resources>
          <jar href="com.example.jar"/>
          <extension name="JavaMail" href="javax.mail.jnlp"/>
     </resources>
...javax.mail.jnlp:
<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.0+" codebase="http://localhost:8080/" href="javax.mail.jnlp">
     <information>
          <title>JavaMail</title>
          <vendor>Sun Microsystems, Inc.</vendor>
          <description>JavaMail API.</description>
          <homepage href="http://java.sun.com/products/javamail/"/>
     </information>
     <security>
          <all-permissions/>
     </security>
     <resources>
          <jar href="javax.mail.jar"/>
          <extension name="JAF" href="javax.activation.jnlp"/>
     </resources>
     <component-desc/>
</jnlp>javax.activation.jnlp:
<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.0+" codebase="http://localhost:8080/" href="javax.activation.jnlp">
     <information>
          <title>JAF</title>
          <vendor>Sun Microsystems, Inc.</vendor>
          <description>JavaBeans Activation Framework extension.</description>
          <homepage href="http://java.sun.com/products/javabeans/glasgow/jaf.html"/>
     </information>
     <security>
          <all-permissions/>
     </security>
     <resources>
          <jar href="lib/javax.activation.jar"/>
     </resources>
     <component-desc/>
</jnlp>Garret