passing IE credentials to sharepoint online using managed code

I am developing a Visual Studio add-in for Outlook that integrates with a Sharepoint Online list. Our Sharepoint site is hosted by Office 365, and our Outlook add-in is using C# CSOM.

I can explicitly create an on-the-fly credential using something like this:

SharePointOnlineCredentials userCredentials = new SharePointOnlineCredentials("me@myDomain.com", objSecurePassword);

but then I have to store the password as an app setting or similar.

If there is already a cookie on the user's computer for the site (created by IE), how can I pass that to the credential object? I want to avoid storing the password in my application's settings.

thanks

joel

Joel