Azure Active Directory has a pretty comprehensive REST & JSON API - the Azure Active Directory Graph API:

https://docs.microsoft.com/en-us/azure/active-directory/deve...

It's recommended to access AAD through the Microsoft Graph API (as opposed to the AAD Graph API) unless it is one of the few scenarios not yet supported on Microsoft Graph. There is a lot of investment in adding new functionality to Microsoft Graph (such as the ability to extend AAD entities with custom, persisted properties on the /beta/ endpoint) and tooling. You can try/prototype out a bunch of your AAD requests in the Graph Explorer without writing code/needing to authenticate for most calls:

https://developer.microsoft.com/en-us/graph/graph-explorer

Ah yes - well spotted. I actually did mean the main Microsoft API rather than the specific AAD one....