This is part of the security system. This helps explain it further:
That said, this shouldn’t trigger the deceptive site warning from google safe search
The more likely reason this is showing is because your sites home page is a fairly generic login page, with no details as to what the site is or what you’re logging into.
I’d recommend adding a landing page with some details about your site, that then links to a login page. I know it seems excessive, but there’s a reason most sites you visit online don’t have their homepage as just a “log in” page