SharePoint Online oAuth - Licensing Cost

Hi everyone,

I have a quick question on SPO's pricing on oAuth. If I were to use a per user plan with MSFT they will charge me in the range of $10 - $20 perhaps depending which package I choose. I wonder if I decide to not use their users and instead take the approach of oAuth and get users signin from their Facebook/Live ID into SharePoint Online, would I save the per user licensing cost then?

Thanks.