CRM Session Sharing facility with external Web Interface

Hi
 We are facing an issue. We have to integrate an external Web Interface to Dynamics CRM 365 v9.1. The Web Interface is developed in Microsoft .Net Framework 4.6 and deployed in Azure IIS. Following are the minimum set of requirements with respect to this Web Interface.
 1)Only Logged-in CRM users should have access to this web interface, with a link/button provided in CRM UI.
2)If the user is not logged in to CRM and tries to access the web interface, we should restrict them.
3)For the logged-in CRM users, then web interface should be able to perform some read and write data operations to CRM objects on behave of this user.
4)We are not allowed to pass user information’s from CRM to Web Interface as  query string.
 
We might be able to achieve these requirements if CRM provides any Session Sharing facility with external Web Interface. Could you please advise us if CRM provides any session sharing facility? If not, is there any other efficient and secured way to achieve these requirements?

Please let me know your views.

Thank you for the support

Davis