code: private String getAuthHeader(HttpServletRequest request, String authType)
        throws HttpAuthenticationException {
      String authHeader = request.getHeader(HttpAuthUtils.AUTHORIZATION);
      // Each http request must have an Authorization header
      if (authHeader == null || authHeader.isEmpty()) {
        throw new HttpAuthenticationException("Authorization header received " +
            "from the client is empty.");
      }
  
      String authHeaderBase64String;
      int beginIndex;
      if (isKerberosAuthMode(authType)) {
        beginIndex = (HttpAuthUtils.NEGOTIATE + " ").length();
      }
      else {
        beginIndex = (HttpAuthUtils.BASIC + " ").length();
      }
      authHeaderBase64String = authHeader.substring(beginIndex);
      // Authorization header must have a payload
      if (authHeaderBase64String == null || authHeaderBase64String.isEmpty()) {
        throw new HttpAuthenticationException("Authorization header received " +
            "from the client does not contain any data.");
      }
      return authHeaderBase64String;
    }
docs: Returns the base64 encoded auth header payload
  @param request
  @param authType
  @return
  @throws HttpAuthenticationException