client.go
func (c *Client) SetAuthHeader(h http.Header) {
	if c.auth != nil {
		h.Set("Authorization", c.auth.String())
	}
}
func (c *Client) SetAuthHeader(h http.Header) {
	if c.auth != nil {
		h.Set("Authorization", c.auth.String())
	}
}
// SetAuthHeader sets client's authorization headers if client
// was configured to work with authorization