Function frame_system::ensure_signed_or_root

pub fn ensure_signed_or_root<OuterOrigin, AccountId>(
    o: OuterOrigin
) -> Result<Option<AccountId>, BadOrigin>where
    OuterOrigin: Into<Result<RawOrigin<AccountId>, OuterOrigin>>,

Ensure that the origin o represents either a signed extrinsic (i.e. transaction) or the root. Returns Ok with the account that signed the extrinsic, None if it was root, or an Err otherwise.