Why not use a cryptocurrency trading bot instead? Like
GunbotI think this option is safer instead of allowing you to access the owner exchange account. There's no need for them to expose their email and password, they just need to give you the API access.
Imagine if I were to give my account, username, and password to someone I didn't know, and that has 0.2 BTC inside it to trade, I wouldn't definitely give it (Unless I'm a whale that could afford something like that amount)
The safest thing to do is have Secured API Access to the account, so that the owner would still be in control and could see all the trades that are being done, etc.