I've developed a REST API back end using Endpoints-Proto-Datastore, which wraps the Cloud Endpoints Python API. I'm starting to look at Qt and trying to get an idea what will be involved in accessing my API from the Qt networking or other library. Might it be nearly as straightforward as is making the calls from the command line using the Python Client library, which even handles OAuth2 flows? This would be very nice. I might use PyQt if this makes things simpler.
I located this document which gives a pretty good overview for my purposes:
"The Google APIs Client Library for C++ will automatically take care of many of the tedious details for interpreting and complying with the discovery documents so that you can write simpler and familiar C++ code."
Now it's a matter of building and installing the C++ client and then figuring out how to generate the client library and access it from a Qt application. But that is beyond the scope of this question.