Auth0 integration with other identity providers

I am building a marketplace that sells vendors access to pages. For example vendors could have SaaS product with the own website. And this vendor SaaS product might also have Auth0 as identity provider. How to integrate our Auth0 with vendor’s Auth0. So for instance after customer buys (he should be already registered and logged in on marketplace) we create an account on a vendor Auth0 if it makes sense.