Trading on behalf

Hello CTrader & community,

I was looking through OpenAPI and found the permission for the App to allow trading on behalf. How is this realized within the OAuth that you're using? Generally, there a client receives a request to access the resource to the grantor, and allows/denies such request. I have created another account and created an app in each to allow access to another account' trading accounts, but was unsuccessful. How can I accomplish this and be able to trade using Account X API key with Account Y broker accounts? 

I've attempted to open https://openapi.ctrader.com/apps/auth?client_id=ACCOUNT_X_CLIENT_ID&redirect_uri=ACCOUNT_X_REDIRECT_URI in Account Y and granting it access for Account X, but for some reason getting HTTP 403 error.

The only way that I've found that I can share account with another user is through CTrader Desktop by using Share option there.

Thank you.