Function signed_body 

pub(crate) fn signed_body(
    api: &str,
    key_file: &str,
    channel: &str,
    op: &ViewOp,
    auth: AuthOptions<'_>,
) -> Value

Signs op on attribution channel channel and builds its submission body.

The op is scoped to the node’s current head first, so the signature is admissible on this log once and nowhere else.