Unfortunately, this information is not available on the provider side.
Why would you be interested in the URL anyway? In practice, as an app service consumer I don't care where my data is coming from as long as I am getting the data that I requested. This open up possibilities for multi providers for single app service. Wouldn't it be nice if the app service can find the closest provider thus creates a faster connection, or if the provider is down it can switch to different provider and still retrieve your data?
Also, by not providing auto-generated documentation on the provider side, it allow us to change the underlying technology for example the data exchange can be JSON instead of SOAP XML.