code: public function getLoginStartUrl($redirecturl) {
  		$facebook = $this->getFacebookObject();
  		
  		$helper = $facebook->getRedirectLoginHelper();
  
  		$permissions = ['email']; // Optional permissions
  		$loginUrl = $helper->getLoginUrl($redirecturl, $permissions);
  
  		return $loginUrl;
  	}
docs: Returns facebook login start auth process
  
  @param string $redirecturl URL where to redirect after login complete