I wonder what it would take to "force" me into doing a social login? It would have to be something drastic, like a website that provides me with needed oxygen.
To get on my hobbyhorse some: what about a platform that your employer uses to distribute relevant documents and updates which you need for your job, which has become sufficiently well-known and implicitly available that hesitating about the dependency is perceived as bizarre?
Note that the response of “don't deal with them then” runs into market information and churn amplification¹ issues when it is a social assumption that picking up a ‘tool’ (which is actually a relationship with a third party, but where this is close to invisible in the steady state) is essentially a free action which requires no consideration, because the information about “does this employer require me to use this tool” neither propagates efficiently nor stays stable.
Past source: wound up changing the email address on one of my Google accounts recently for exactly that reason. They actually asked me up-front whether I had a GMail account they could use instead, which turned out to be because they use restricted Google Docs for critical material. Not naming them, but in a broad sense, this is one of the more ethical companies I've ever dealt with, by the way.
Future source: I should probably be considering digging into LinkedIn soon despite their past abusive behaviors, because as it turns out, if I want to dig myself out of this hole…
¹ I assume there's a ‘real’ term for what I'm thinking of, but I don't know what it is, so I cobbled that one together out of the most relevant-seeming bits.