What is this technology called? An API, OAuth? I'm trying to do some research on how this works but I'm not sure what I should be researching.
Social login and SSO is generally implemented these days as OIDC (which is based on oauth2). You can read the RFCs for it, and they pretty much explain the whole thing.
Oauth2: https://tools.ietf.org/html/rfc6749
PKCE (replaces the implicit flow): https://tools.ietf.org/html/rfc7636
OIDC: https://openid.net/specs/openid-connect-core-1_0.html
They don't always make it obvious, but it is usually OAuth2, sometimes with tweaks
Social login and SSO is generally implemented these days as OIDC (which is based on oauth2). You can read the RFCs for it, and they pretty much explain the whole thing.
Oauth2: https://tools.ietf.org/html/rfc6749
PKCE (replaces the implicit flow): https://tools.ietf.org/html/rfc7636
OIDC: https://openid.net/specs/openid-connect-core-1_0.html