How to use create ExchangeService with TokenCredentials?

Question

I wanted to use the EWS Managed API in my Office Mail App.  I would like to obtain the credential from the mailbox in JS and then pass it to the code behind to create the
Microsoft.Exchange.WebServices.Data.ExchangeService
object.  I was able to create the object if I use the WebCredential with username and password, but I would like to use the credential in the mailbox, so I don't have to ask the user for username and password again.  I saw that there
is an identitytoken available in JS
Office.initialize = function () {
// Checks for the DOM to load using the jQuery ready function.
$(document).ready(function () {
// After the DOM is loaded, app-specific code can run.
_mailbox = Office.context.mailbox;
_mailbox.getUserIdentityTokenAsync(getUserIdentityTokenCallback);
_Item = _mailbox.item;
$(mailID).val(_Item.itemId);
$(url).val(_mailbox.ewsUrl);
function getUserIdentityTokenCallback(asyncResult) {
$(token).val(asyncResult.value);
so, I tried to use this token to create the ExchangeService object and get the mail item like below.
public Item Test(string email, string token, string mailID, string url)
ServicePointManager.ServerCertificateValidationCallback = CertificateValidationCallBack;
exchangeService = new ExchangeService(ExchangeVersion.Exchange2013_SP1);
exchangeService.Credentials = new TokenCredentials(token);
exchangeService.TraceEnabled = true;
exchangeService.TraceFlags = TraceFlags.All;
exchangeService.Url = new Uri(url);
Item item = null;
try
item = this.GetEmail(mailID);
catch (Exception ex)
string a;
return item;
public Item GetEmail(string mailID)
if (!string.IsNullOrEmpty(mailID))
Logger.ErrorLog("GetEmail: mailID =" + mailID);
ItemId itemID = new ItemId(mailID);
Item emailItem = Item.Bind(exchangeService, itemID);
emailItem.Load(new PropertySet(Exchange.BasePropertySet.FirstClassProperties, ItemSchema.MimeContent));
return emailItem;
else
throw new Exception("mailID is null or empty");
I get the following exception:
"The request failed. The remote server returned an error: (401) Unauthorized."}
on  Item emailItem = Item.Bind(exchangeService, itemID); in the GetEmail function.  How do I properly retrieve tokens in JS in the mailbox to create a EWS Managed API ExchangeServices?
Thank, Hilda

Answer 1

Ok, I got it to work with "getCallbackTokenAsync".  Use the token that this function delivers and attach to Exchange services with it like so... (I persist the token I receive for all future communications in a global var)
try
ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2013)
Credentials = new OAuthCredentials(in.cnxToken),
Url = new Uri(in.uriEws)
ItemId itemID = new ItemId(in.itemId);
message = Item.Bind(service, itemID);
catch (Exception ex)
eaResp.status = "Error: Exchange GetItem failed.\n" + ex.Message.ToString();
return eaResp;