To use Gmail with KHS (or FSG), turn on 2-Step verification and then use the steps below to create a app specific password to use in KHS instead of your normal one.
Click this link to go directly to the security page on Google: https://myaccount.google.com/security
Under Signing in to Google, turn on 2-Step Verification then choose the arrow next to the App passwords, and provide your password if asked.
On the App passwords page, in the Select app drop-down choose Other (custom name).
Note the app password under Your app password for your device. You can use this with your Gmail address in the app you are connecting to your Gmail account (or adding your Gmail account to). This combination grants complete access to your Gmail account by the app that is using it. After you have entered the app password, you do not have to remember it.
Important: The 16-character app password is displayed with spaces so it is easier to read. When you enter it to the app you want to connect, ignore the spaces and enter it as an unbroken string of 16 characters.