I'm trying to write an Ant script to retrieve an URL via port tunnelling.

It works great when I use a password (the names xxxx'd out for privacy):

<project default="main">
  <target name="main">
    <sshsession host="xxxx"
    username="xxxx"
    password="xxxx">
      <LocalTunnel lport="1080" rhost="xxxx" rport="80"/>
      <sequential>
        <get src="http://localhost:1080/xxxx" dest="/tmp/xxxx"/>
      </sequential>
    </sshsession>
  </target>
</project>

But it doesn't work when I use a keyfile, like this:

    <sshsession host="xxxx"
    username="xxxx"
    keyfile="/Users/xxxx/.ssh/id_dsa"
    passphrase="xxxx">
      <LocalTunnel lport="1080" rhost="xxxx" rport="80"/>
      <sequential>
        <get src="http://localhost:1080/xxxx" dest="/tmp/xxxx"/>
      </sequential>
    </sshsession>

I get this exception:

/tmp/build.xml:8: com.jcraft.jsch.JSchException: Auth cancel
    at com.jcraft.jsch.Session.connect(Session.java:451)
    at com.jcraft.jsch.Session.connect(Session.java:150)
    at org.apache.tools.ant.taskdefs.optional.ssh.SSHBase.openSession(SSHBase.java:223)

• I'm sure I'm using the correct keyfile (I've tried using the wrong name, which gives a legitimate FileNotFoundException).
• I can successfully ssh from the command line without being prompted for a password.
• I'm sure I'm using the correct passphrase for the keyfile.

What's the cause of this error and what can I do about it?