protected void doTokenAuth(AuthToken token, HttpServletRequest request, HttpServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        AuthPrincipal principal = new AuthPrincipal(token.getPrincipal());
        principal.addRoles(token.getRoles());
        doFilterChain(request, response, chain, principal);
    }
Implements token based authentication.  This simply creates a principal from the {@link AuthToken}
and then calls doFilterChain.
@param token the token
@param request the request
@param response the response
@param chain the filterchain
@throws IOException when I/O failure occurs in filter chain
@throws ServletException when servlet exception occurs during auth
common/servlet/src/main/java/io/apiman/common/servlet/AuthenticationFilter.java