title: AADSTS50020: User account does not exist in tenant
body: <p>I was able to register an app created by another tenant as an enterprise app of my own tenant.
  I signed in to the app as a user, but I got the following error.</p>
  <hr />
  <p>AADSTS50020: User account 'test001@testdomain001.onmicrosoft.com' from identity provider 'https://sts.windows.net/aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee/' does not exist in tenant 'testdomain002' and cannot access the application '55555555-6666-7777-8888-999999999999'(OneDriveAPIBrowser_test001) in that tenant.
  The account needs to be added as an external user in the tenant first.
  Sign out and sign in again with a different Azure Active Directory user account.</p>
  <hr />
  <p>How can a user of another tenant use it without the application creator tenant performing any processing?</p>