I want to develop an add in for Outlook which after click on button forward selected email to hardcoded address. What I find is that I must use Graph API to do this, but I lost in documentation on how I get token to make an API call. In Outlook API it is simple as call getCallbackTokenAsync. Is it similar way to get token for Graph API? What is the simplest way of getting this token, best if it could be done without user interaction?
It's straightforward. First you need to register you application in Azure AD, make sure you provide right roles/permissions so that you can get a token. Using the token you can access a protected resource like Microsoft Graph API. You may want to get it started following the documentation/javascript sample.