I'm hoping this may be of use - I had ocassion to get data for a customer from the graph API on the Azure B2C service and I needed to use Oauth 2.0 to authenticate to get this data.
I achieved this by using a simple azure function the take a clientID and secret and perform the OAuth get token and submit token in the azure function - so a single call to the function gets the graph api data protected by Oauth 2.0.
The code is in Node.js which is natively supported in azure functions and I guess you could host it elsewhere if you required.
See https://github.com/djburnham/graph-api-azure-fn-proxy for the code.
I hope this helps.
Kind regards,
David.
BTW I included my voice in the requests to the dev team to include this functionality in the PowerBi product.