ASP.NET Core API Facebook注册/登录

Question

I'm working on ASP.NET Core API and need to add option to register with social service, eg Facebook. Scenario should be eg Android App user should click "Sign up with Facebook" at startup, then Facebook app should open then user should click confirm and be registered in app.

Default Asp.net web example shows how to do it with web page on same host as APIs with return Challenge() response that basically returns HTML page as I understood.

What is the correct flow here and is there any existing libraries to do that? As I understand now flow is something like this: 1. API server has my AppId and AppSecret from Facebook 2. Android app should request "applciation token" from API server 3. Android app should call Facebook with that token and get "user confirmation token" 4. Android app should pass "user confirmation token" to API server 5. API server should call Facebook with "AppId/AppSecret token + user confrimation token" and get details about user and create local user in database. 6. API server should create "API token" for that user 7. Android app should use "API token"

So at least I want to understand what to replace this code from example with:

public IActionResult ExternalLogin(string provider, string returnUrl = null) {
   // Request a redirect to the external login provider.
   var redirectUrl = Url.Action("ExternalLoginCallback", "Account", new { ReturnUrl = returnUrl });
   var properties = signInManager.ConfigureExternalAuthenticationProperties(provider, redirectUrl);
   return Challenge(properties, provider);

Answer 1

the thing to understand is the default web app template provided in VS 2015 uses ASP.NET Identity with cookie authentication. cookie auth works for web browsers but for an android app to authenticate you would need something to issue jwt tokens in addition to or instead of cookies. There is nothing built in provided by Microsoft for that in asp.net core, the recommendation is to use IdentityServer4