1) Password protect site. 2) Issue URLs that 'auto login'

I’m creating a website for my wedding. There will be some personal information in the site that I don’t want to share with the entire web. I’d like to protect the entire site and then issue each guest with a unique username and password to gain access to the site. I’d like to provide users with a URL that contains the login credentials for the site – i.e. the user clicks the URL and is automatically logged into the site as a ‘subscriber’.

Is this possible? What is the easiest and most secure method?