code: @Nullable
    public static DigestAuthClientCredentials getDigestAuthClientCredentials (@Nonnull final HttpServletRequest aHttpRequest)
    {
      ValueEnforcer.notNull (aHttpRequest, "HttpRequest");
  
      final String sHeaderValue = aHttpRequest.getHeader (CHttpHeader.AUTHORIZATION);
      return HttpDigestAuth.getDigestAuthClientCredentials (sHeaderValue);
    }
docs: Get the Digest authentication credentials from the passed HTTP servlet
  request from the HTTP header {@link CHttpHeader#AUTHORIZATION}.
  
  @param aHttpRequest
  The HTTP request to be interpreted. May be <code>null</code>.
  @return <code>null</code> if the passed request does not contain a valid
  HTTP Digest Authentication header value.