From https://stackoverflow.com/questions/30188226/creating-asana-tasks-from-google-apps-script

Create Asana Task from google apps script

/*************************
 * Asana     Functions    *
 *************************/

// first Global constants ... Key Ids / tokens etc.
PERSONAL_ACCESS_TOKEN = "0/d3c41c435b0c3f70b399999952edee5";  // Put your unique Personal access token here
WORKSPACE_ID = "49489999934875"; // Put in the main workspace key you want to access (you can copy from asana web address)
ASSIGNEE = "jondoe@nomail.com";  // put in the e-mail addresss you use to log into asana


// ** testTask() **  is useful for using as a Debug start point.  "select function" on script editor menu
// choose "testTask" then debug functionality is enabled

function testTask() {
    quickTask("a quick task")  
};


// ** quickTask(taskName) ** Made a short function so I could just add simple tasks easily
function quickTask(taskName) {
    var newTask = {
    name: taskName,
    workspace: WORKSPACE_ID,
    project: "",       // if you have a project you like to add add it here
    assignee: "me"     // Me is understood by asana
  };
  createAsanaTask(newTask);

};

/******************************************************************************************
 **  createAsanaTask(task) **
 ************************ 
 * creates a new asana task with information (like task name, project, notes etc.) contained in  
 * the  object 'newTask" passed to it.
 * 'task' should be of the format an object with option pairs that match the Asana task
 * key parameters, as many or as few as you want.
 * e.g. 
 * var newTask = {
 *   name: taskName,
 *   workspace: WORKSPACE_ID,
 *   project: "My Project",       // if you have a project you like to add add it here
 *   assignee: "JohnDoe@madeupmail.com"     // person the task should be assigned to.
 * }
 *  you could add other info like due dates etc.
 * it returns a "task" object containing all asana task elements of the one task created including the id.
 *************************************************************************************************/   



function createAsanaTask(task) {

    // when creating an Asana task you must have at least a workspace id and an assignee
    // this routine checks if you defined one in the argument you passed
if (task.workspace == null) {
    task.workspace=WORKSPACE_ID
    }
if (task.assignee == null) {
    task.assignee="me";
    }

 /* first setup  the "options" object with the following key elements:
 *
 *   method: can be GET,POST typically
 *
 *   headers: object containing header option pairs
 *                    "Accept": "application/json",        // accept JSON format
*                    "Content-Type": "application/json",  //content I'm passing is JSON format
*                    "Authorization": "Bearer " + PERSONAL_ACCESS_TOKEN // authorisation
*  the authorisation aspect took me ages to figure out.
*  for small apps like this use the Personal Access Token method.
*  the important thing is to use the Authorization option in the header with the 
*  parameter of  "Bearer " + PERSONAL_ACCESS_TOKEN
*  the PERSONAL_ACCESS_TOKEN  is exactly the string as given to you in the Asana Web app at
*  the time of registering a Personal Access Token.  it DOES NOT need any further authorisation / exchanges
*  NOR does it needo any encoding in base 64 or any colon.
*
*  payload: this can be an object with option pairs  required for each element to be created... in this case 
*           its the task elements as passed to this function in the argument "task" object.
*            I found it doesn't need stringifying or anything.   
*
       ********************************************************************************************************/      

var options = {
    "method": "POST",
    "headers": {
        "Accept": "application/json",
        "Content-Type": "application/json",
        "Authorization": "Bearer " + PERSONAL_ACCESS_TOKEN
               },
        "payload": task
        };
  // using try to capture errors 
try {
                          // set the base url to appropriate endpoint - 
                          // this case is "https://app.asana.com/api/1.0"  plus "/tasks"
                          // note workspace id or project id not in base url as they are in the payload options
                          // use asana API reference for the requirements for each method
var url = "https://app.asana.com/api/1.0/tasks";
                          // using url of endpoint and options object do a urlfetch.
                          // this returns an object that contains JSON data structure into the 'result' variable 
                          // see below for sample structure
var result = UrlFetchApp.fetch(url, options);
                          // 
var taskJSON = result.getContentText();
} catch (e) {
        Logger.log(e);
        return null;
} finally {
 // parse the result text with JSON format to get object, then get the "data" element from that object and return it.
 // this will be an object containing all the elements of the task.
    return JSON.parse(taskJSON).data;
    }
};