public String getSessionTokenFromString(String requestQuery) {
OAuthSigner signer = null;
try {
// Step 7. Exchange authorized request token for access token.
signer = new OAuthRsaSha1Signer(getPrivateKey());
GoogleOAuthHelper oauthHelper = new GoogleOAuthHelper(signer);
oauthHelper.getOAuthParametersFromCallback(requestQuery, oAuthParameters);
// Step 8. Upgrade to access token.
return oauthHelper.getAccessToken(oAuthParameters);