code: func (sp *ServiceProvider) MakeRedirectAuthenticationRequest(relayState string) (*url.URL, error) {
  	req, err := sp.MakeAuthenticationRequest(sp.GetSSOBindingLocation(HTTPRedirectBinding))
  	if err != nil {
  		return nil, err
  	}
  	return req.Redirect(relayState), nil
  }
docs: // MakeRedirectAuthenticationRequest creates a SAML authentication request using
  // the HTTP-Redirect binding. It returns a URL that we will redirect the user to
  // in order to start the auth process.