Hi William,
>>However, when i try to replace 'me' with another user, i get 'Access Denied'<<
What kind of user did you mean? Did these users on the same Azure AD the app you register? If not, this result is expected.
And there is a new authenticate mode named V2.0(preview) which allow the app signing in Microsoft account and Azure AD users with a single authentication model. You can get more detail about this topic from link below:
Authenticate Office 365 and Outlook.com APIs using the v2.0 app model preview
This forum is mainly for discussing issues related to Office add-ins development. For this question, I would suggest you asking a question in Stack Overflow and tag your questions with [office365].
The reason why I recommend posting appropriately is you will get the most qualified pool of respondents, and Office 365 developer team will also monitor the tag regularly.
Thanks for your understanding.
Regards & Fei
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