Google Apps 2 legged OAuth of Google Calendar API with Google Apps Script. Please import oauth.js and sha1.js from http://code.google.com/p/oauth/. if you happen any problem,Please modify oauth.js to below oauth.js code.

main.js

function twoleggedOAuth() {

  var action = "https://www.google.com/calendar/feeds/default/private/full?xoauth_requestor_id={user mail address}";
  var accessor = { consumerSecret: '{consumerSecret}' };
  var message = { method: 'get', action: action, parameters: {}, };
  OAuth.setParameter(message, 'oauth_version', '1.0');
  OAuth.setParameter(message, 'oauth_nonce', OAuth.nonce(32));
  OAuth.setParameter(message, 'oauth_timestamp', OAuth.timestamp());
  OAuth.setParameter(message, 'oauth_consumer_key', '{your domain}');
  OAuth.SignatureMethod.sign(message, accessor);
  var val = OAuth.getAuthorizationHeader(null,message.parameters);

  var option =
      {"method": message.method,
       headers : {"Authorization" : val,"GData-Version" : "2.0"}
      };

  //Send Request
  try {
    var res = UrlFetchApp.fetch(action, option);
  } catch(e) {
    e.message.match(/&gsessionid=(.+) に/); //get gsessionid,But it's japanese locale. if you need any another local,please hack error responce.
    var gsessionid = RegExp.$1;
    var m2 = { method: 'get', action: action, parameters: {"gsessionid": gsessionid}};
    OAuth.setParameter(m2, 'oauth_version', '1.0');
    OAuth.setParameter(m2, 'oauth_nonce', OAuth.nonce(32));
    OAuth.setParameter(m2, 'oauth_timestamp', OAuth.timestamp());
    OAuth.setParameter(m2, 'oauth_consumer_key', '{your domain}');
    OAuth.SignatureMethod.sign(m2, accessor);
    var val2 = OAuth.getAuthorizationHeader(null,m2.parameters);
    action += "&gsessionid=" + gsessionid;
    Logger.log(val2);
    Logger.log(action);
    
    option = {
      "method": m2.method,
       headers : {"Authorization" : val2,"GData-Version" : "2.0"}
    };
    res = UrlFetchApp.fetch(action , option);
  }
    
  
  //display
  var test = res.getContentText("UTF-8");
  Logger.log(test);
}

oauth.js

//on oauth.js OAuth class.
    getAuthorizationHeader: function getAuthorizationHeader(realm, parameters) {
        var header = 'OAuth ';
        if(realm != null) header += 'realm="' + OAuth.percentEncode(realm) + '"';
        var list = OAuth.getParameterList(parameters);
        for (var p = 0; p < list.length; ++p) {
            var parameter = list[p];
            var name = parameter[0];
            if (name.indexOf("oauth_") == 0) {
              header += OAuth.percentEncode(name) + '="' + OAuth.percentEncode(parameter[1]) + '"';
              if(p < list.length -1) {
                header +=  ', ';
              }
            }
        }
        return header;
    }

//

OAuth.nonce.CHARS = "0123456789abcdef";