code: public String getProxyFile() {
  	String location;
  	location = System.getProperty("X509_USER_PROXY");
  	if (location != null) {
  	    return location;
  	}
  	location = getProperty("proxy");
  	if (location != null) {
  	    return location;
  	}
  	return ConfigUtil.discoverProxyLocation();
      }
docs: Retrieves the location of the proxy file.
  It first checks the X509_USER_PROXY system property. If the property
  is not set, it checks next the 'proxy' property in the current
  configuration. If that property is not set, then it defaults to a
  value based on the following rules: <BR>
  If a UID system property is set, and running on a Unix machine it
  returns /tmp/x509up_u${UID}. If any other machine then Unix, it returns
  ${tempdir}/x509up_u${UID}, where tempdir is a platform-specific
  temporary directory as indicated by the java.io.tmpdir system property.
  If a UID system property is not set, the username will be used instead
  of the UID. That is, it returns ${tempdir}/x509up_u_${username}
  <BR>
  This is done this way because Java is not able to obtain the current
  uid.
  
  @return <code>String</code> the location of the proxy file