Custom app access to to other custom apps

Hello, 

You will either need to obtain an access token for a user that already has access to the content or, if a JWT app, add the service account as a collaborator on the content. You can get the email address of the service account by making a call to the get current user endpoint. Then, collaborate this email on the content just like you would any other user. 

Best,

Kourtney, Box Developer Advocate