Thanks for contacting the Ad Manager API team.
There is a possibility to access the API within your own implementation, however, kindly note that we're unable to assist you on creating a custom implementation of our client libraries.
If you haven't checked out our guide yet on the Reporting Basics, kindly do so as it shows you how to run and download a report with the API. It covers both using an existing saved report query, and creating an ad hoc report query. Within the guide, there's also a section in which it details how to Read the Report Data which is a useful reference if you're using our supported client libraries. You can also refer here for our sample code on retrieving a saved report query in Java.
Lastly, you can always check out our guide to Authentication for any clarifications on authenticating with the API.