Hello, thank you for reaching out. QuantConnect integrates with Interactive Brokers using the TWS API over their customer LEAN Engine to the Trader Workstation. You can read more about the LEAN Engine system here: https://www.ibkrcampusdev.wpengine.com/campus/ibkr-quant-news/lean-engine-on-aws-and-interactive-brokers-guide/. As stated in the Quant Connect documentation, provided credentials are saved in their Lean Configuration File: https://www.quantconnect.com/docs/v2/lean-cli/datasets/brokerages#07-Research.

In the process of connecting Interactive Brokers to QuantConnect, you are providing your credentials to log in to their locally hosted IB Gateway system. These details were provided by Jared Broad, QuantConnect CEO, earlier this year as described in https://www.quantconnect.com/forum/discussion/16471/live-trading-with-ib/.

We hope this helps!