> Either way, how can you make it a requirement to provide, what is not a requirement to have?
You simply make it a requirement to provide it if you have it. That is not the same as optional. If its optional then you aren't lying to immigration if you leave it blank. If it is not optional then you are.
Huge, massive amounts of people are like this. Huge. Twitter, Facebook, others have massively inflated usage numbers.
I suspect people with social media logins are the minority in the US, for example.
Doubt me? Do you think most people's 68 year old parents, or grandparents, all have logins?
Either way, how can you make it a requirement to provide, what is not a requirement to have?