I would (almost) never use a site that only allowed... If you're a business customer, you'll use whatever auth system is presented. And 80% of the time Google

I would (almost) never use a site that only allowed... If you're a business customer, you'll use whatever auth system is presented. And 80% of the time Google login is perfect; the other 20% will deal. "Oh, your product will save me thousands of dollars? But it requires a Google account? Sorry, can't use it"... said nobody, ever. There's a huge difference between B2B and B2C customers, and you need to understand which business you're in. Yeah, if you're trying to accommodate the mass market, you need all the options. If you have a niche product that makes money for people, you should spend all your time working on features that make people money. Auth is not one of them.