In almost all social networking APIs it is necessary to authenticate your app with OAuth, in order to use the features of it.
How is this process?
In my case, I'm trying to get a list of the followers of a particular blog via the Tumblr API v2, using the Javascript client: link
I tried to find some solution in the oauth.net documentation but everything went pretty confusing for me.
In a google search I found some things that can help you understand how it works and how it is, in Diogo's blog has an explanation to better detail what it is and how it works at first sight is very complicated even because one little to what we are accustomed to doing "simple login screens and password."
Explanation of what works (Blog Diogo)
In the case of tumblr does not have much difference of twitter or facebook, giving a researched in google I found some examples in php and javascript that can help you, I think it is easier to see the code and run to understand faster.
In the links you have enough example, and also this plugin for wordpress that can help you too.
1 - Javascript API Thumblr and Documentation
2 - PHP API Thumblr and Documentation
3 - Wordpress Plugin
