New Wordpress plugin - authentication is needed

I write a new plugin that will work against an external application.

This application need an access to this plugin, and will create, edit and delete posts.

Of course I want to protect the plugin so only the external application will be able to access it. I couldn't find any native oauth authentication and/or api for wordpress, and I don't want to force users to install another plugin, as oAuth2.

I found this one, but looks like it is relevant only for wordpress.com, and not an internal wordpress feature: http://ift.tt/13JciTt

I need some simple and safe solution, thanks!!