code: @Override
      public @Nullable String getPassword( @Nonnull String instanceId ) throws InternalException, CloudException {
          APITrace.begin(getProvider(), "getPassword");
          try {
              return new GetPassCallable(instanceId, getProvider()).call();
          } catch( CloudException ce ) {
              throw ce;
          } catch( Exception e ) {
              throw new InternalException(e);
          } finally {
              APITrace.end();
          }
      }
docs: Get encrypted initial Windows password. This method only definitely works with standard Amazon AMIs:
  http://aws.amazon.com/windows/amis/
  Other AMIs in the public library may have had their password changed, and it will not be retrievable on instances
  launched from those.
  
  @param instanceId
  @return
  @throws InternalException
  @throws CloudException