Function browser_carries 

pub fn browser_carries(redirect_uri: &str, mode: ResponseMode) -> bool

Whether a browser carries a sign-in’s code to its client: every redirect but a loopback one taking its code in the query.

That one goes to a listener on the host that approved the sign-in, and what approved it fetches it there, as didbot_agentd::loopback::deliver does. An approval holds any other for the authorize page to hand to a browser signed in as the account.