WorkOS pricing for B2B apps is untenable however. Same with Auth0. Is there any cost effective SaaS auth solution which allows multiple customer SSO integrations besides Microsoft Entra ID for External?

Agreed, Firebase is the worst. Google's impenetrable documentation, paired with frequent breaking changes, opaque pricing model (paired with asking for your card details but not letting you set a limit at which the app should turn off), trigger-happy product sunsetting, etc. etc. should be enough to turn anyone away.

And this isn't even getting started on how bad the DX is in general. I have found Pocketbase to be so much easier for basic auth (obviously it's too simplistic if you need major scale SSO solutions...)