Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother, thank you for your question and for your interest to follow the rulings of Islam concerning your financial dealings.
This kind of transaction is called tawrruq which is impermissible. As for working in an Islamic bank, it is allowed on the condition that you avoid signing such transactions.
Responding to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, stated,
Islamic banks lend people in a way called tawarruq; they buy a commodity from any market, sell it on credit to the customer and then sell it for cash in the market back to give him the cash. They claim that this is permissible.
The OIC (Organization of Islamic Conference) Fiqh Academy said clearly in a decision issued in 2009 that this is unlawful (haram) and pure riba. It is not permissible for any Muslim to take this kind of loan.
It is also wrong for the Islamic bank to do this, but it is not haram to work in an Islamic bank; just do not accept to do this kind of transaction. The same applies to the advance on salary.
Allah Almighty knows best.