I have two sites (web apps) in Azure, written under ASP NET. I want to implement such a scenario: a user registers on one of them and then, being authorized, gets the opportunity to interact with him through the other, i.e. Site 2 receives an "access token" (analogy with the OAuth protocol) from site 1, through which it will be possible to change the state on site 1 and display the result of the operation on site 2.
My question is quite general: how can this be realized, in the direction of which to "dig"? I have no serious experience in writing API, so I get scared when choosing between the OAuth server, the Azure Management API, the Azure API apps. What is the best fit?