First of all try to avoid using self implemented methods. Most commonly used approach is to use Json web token. https://jwt.io/ There for when you log in, return Token to angular2 and then pass it on every request. There are many examples of implementation and libraries to be used. https://github.com/auth0/angular2-jwt

How to use JWT in MVC application for authentication and authorization?

Best way is using a package called IdentityServer. I have written a tutorial on it but using one of its older versions, however it will give you a good idea:

Securing .Net Core Web API with IdentityServer4 (Resource Owner flow); using SQL Server db, enabling refresh tokens and external login - Part 1