I've been using WorkOS for my SaaS products and I'm pretty satisfied with it. It's straightforward to set up Google/Microsoft/MagicLink (free), including staging and production environments. The best part, though, is that it lets my enterprise customers configure their own SAML/OpenID Connect IDPs.

I get charged per connection, so I just pass that cost onto my customers. As a solo developer, I'd have a hard time supporting so many IDPs with a unified API without this.

They did recently hike up the cost per connection, but they're giving a one-year extension at the old rates, which seems fair.