@Nullable @Override public OAuth2Token apply(HttpHeaders headers) { final String authorization = headers.get(header); if (Strings.isNullOrEmpty(authorization)) { return null; } final Matcher matcher = AUTHORIZATION_HEADER_PATTERN.matcher(authorization); if (!matcher.matches()) { logger.warn("Invalid authorization header: " + authorization); return null; } return OAuth2Token.of(matcher.group("accessToken")); } }