Wordpress - Integrating custom web application
After consulting with someone who's developed with Wordpress before, he recommended to build a plugin.  And since I have no experience with Wordpress, he helped me build it.  It was literally 3 lines of PHP.
Thank you all.
I was tasked to create a file upload workflow that integrates with Wordpress.  
I created a backend that is called via REST that does a lot of custom workflows. Thus, I cannot use the current plugins.
It is a single page application that accepts a file as well as some metadata.
My current dilemma:  I need to integrate this web application within Wordpress and have no clue where to start.