Function client_id 

pub fn client_id(cfg: &ClientConfig) -> String

The client’s identity.

In production this is the URL of the metadata document itself, which the PDS fetches. In dev it is atproto’s localhost development client: the literal http://localhost with the redirect and scope in the query string.

Both query parameters are percent-encoded by the serializer rather than interpolated. redirect_uri contains : and /, and any & or ? in a configured value would otherwise splice additional parameters into the client_id — a config value must never be able to redefine the redirect.