protected Properties getConfiguration() {
    return config;
  }
@Test
  public void testGetConfiguration() throws Exception {
    AuthenticationFilter filter = new AuthenticationFilter();
    FilterConfig config = Mockito.mock(FilterConfig.class);
    Mockito.when(config.getInitParameter(AuthenticationFilter.CONFIG_PREFIX)).thenReturn("");
    Mockito.when(config.getInitParameter("a")).thenReturn("A");
    Mockito.when(config.getInitParameterNames()).thenReturn(new Vector<String>(Arrays.asList("a")).elements());
    Properties props = filter.getConfiguration("", config);
    Assert.assertEquals("A", props.getProperty("a"));

    config = Mockito.mock(FilterConfig.class);
    Mockito.when(config.getInitParameter(AuthenticationFilter.CONFIG_PREFIX)).thenReturn("foo");
    Mockito.when(config.getInitParameter("foo.a")).thenReturn("A");
    Mockito.when(config.getInitParameterNames()).thenReturn(new Vector<String>(Arrays.asList("foo.a")).elements());
    props = filter.getConfiguration("foo.", config);
    Assert.assertEquals("A", props.getProperty("a"));
  }