String refreshToken = requestMessage.getParameter(OAuth2.REFRESH_TOKEN);
if(refreshToken == null){
OAuth2ProblemException problem = new OAuth2ProblemException(OAuth2.ErrorCode.INVALID_REQUEST);
throw problem;
}
OAuth2Accessor accessor = null;
for (OAuth2Accessor a : SampleOAuth2Provider.ALL_TOKENS) {
if(a.refreshToken != null) {
if (a.refreshToken.equals(refreshToken)) {
accessor = a;
break;