public function usingHeader(string $key, $value): self
    {
        $this->headers->put($key, $value);
        return $this;
    }
public function usingHeader(string $key, $value): self
    {
        $this->headers->put($key, $value);
        return $this;
    }
public function usingHeader ( string $ key , $ value ) : self { $ this -> headers -> put ( $ key , $ value ) ; return $ this ; }
adds any arbitrary header

@api
@param   string  $key    name of header
@param   string  $value  value of header
@return  \stubbles\peer\http\HttpConnection
adds any arbitrary header