Base URL this route is mounted at, e.g. "https://yourapp.com/api/social". Each provider's redirect URI is <endpoint>/<platform lowercased> and must be registered with that platform verbatim.
Return a string to show as an error (redirects to errorRedirectURL); return void on success.
Where a successful connect lands, unless the start request carried returnTo.
OptionalscopesPer-platform permissions; each provider has its own default.
Options for setupSocialAuth.