Different people use various items. You can do direct partnerships, as I've seen our vendors do with Duo, or you can roll your own ADFS, as I spoke with a company yesterday that was doing. If you're comparing options, I'd also look at Okta.

Go talk to the people who make identity products and ask them to sell it to you. It appears that you have no idea what you're asking, so it's either that or hire a consultant to tell you.