The API for java.net.Authenticator.setDefault does not allow the
default authenticator to be changed. This makes the API unusable in
a scenario where Java Web Start is used.

Java Web Start installs a default authenticator when it starts up
since it might get proxy authentication requests when it starts
downloading the users application from the network.

Later, when the control is transfered to the actual application (still
running in the same JVM), then the application might want to install
its own authenticator. This is currently impossible.

The customer request is described in bug 4411606