Pulling current post/page data into header.php

I want to pull some post/page specific data (author name, post ID, publish time, etc) into header.php to be used in meta tags. I am having trouble figuring out the most efficient way to do this. It is my understanding that I will need to create a loop within header.php to pull this data. How can I go about creating a loop for the current page/post if I don’t yet know the ID?