code: public static boolean checkAuthentication(SipServletRequest request, DaoManager storage, Sid organizationSid) throws IOException {
          // Make sure we force clients to authenticate.
          final String authorization = request.getHeader("Proxy-Authorization");
          final String method = request.getMethod();
          if (authorization == null || !CallControlHelper.permitted(authorization, method, storage, organizationSid)) {
              if (logger.isDebugEnabled()) {
                  String msg = String.format("Either authorization header is null [if(authorization==null) evaluates %s], or CallControlHelper.permitted() method failed, will send \"407 Proxy Authentication required\"", authorization==null);
                  logger.debug(msg);
              }
              authenticate(request, storage.getOrganizationsDao().getOrganization(organizationSid).getDomainName());
              return false;
          } else {
              return true;
          }
      }
docs: Check if a client is authenticated. If so, return true. Otherwise request authentication and return false;
  @param request
  @param storage
  @param organizationSid
  @return
  @throws IOException