I have a number of IDP (ADFS, identityserver, …) that require social logins (Facebook, Twitter etc.)
Auth0 has a large range of social logins.
This article - https://auth0.com/docs/protocols/saml/saml-idp-generic - shows how to use Auth0 as a generic IDP that I can get to from my Identity providers (in this scenario acting as an SP).
The piece I’m missing is how to get to the Auth0 social logins?
The path would be:
App → My IDP → SAML → Auth0 → Auth0 social
If I understood the situation correctly then like you mentioned the other identity providers would be acting as service providers and Auth0 as a SAML identity provider. In this situation, you would have to represent the service provider as a client application with the SAML 2.0 addon enabled.
By performing the above the service provider would redirect to Auth0 and any connection enabled for the respective client application would be a possible method of authentication (this would include social connections). If the end-user authentication with Facebook, for example, then the Facebook profile information would be mapped to a SAML assertion sent to the service provider and in accordance with the SAML addon settings you configured.
Correct.
Figured this out yesterday :-).
When my IDP redirects to Auth0, the Auth0 Lock screen appears with the social connections that I configured (as you predicted).