Is the Zapier integration with Webflow secure?

Yes. Zapier uses oAuth to interface with your Webflow account (the same way Facebook and Google connect with their accounts).

If you are already logged in to your Webflow account when you integrate with Zapier, Webflow will not require you to reenter your password and will present you with an authorization screen immediately. 

NOTE: Zapier does not have access to any of your account information, including your password.