Resolved #4927: Document social logins.

docs/en/Authentication/Social-External-Logins.md

@@ -0,0 +1,30 @@
+# Social/External Logins
+
+## ASP.NET Core MVC / Razor Pages UI
+
+The [Account Module](../Modules/Account.md) has already configured to handle social or external logins out of the box. You can follow the ASP.NET Core documentation to add a social/external login provider to your application.
+
+### Example: Facebook Authentication
+
+Follow the [ASP.NET Core Facebook integration document](https://docs.microsoft.com/en-us/aspnet/core/security/authentication/social/facebook-logins) to support the Facebook login for your application.
+
+#### Add the NuGet Package
+
+Add the [Microsoft.AspNetCore.Authentication.Facebook](https://www.nuget.org/packages/Microsoft.AspNetCore.Authentication.Facebook) package to your project. Based on your architecture, this can be `.Web`, `.IdentityServer` (for tiered setup) or `.Host` project.
+
+#### Configure the Provider
+
+Use the `.AddFacebook(...)` extension method in the `ConfigureServices` method of your [module](../Module-Development-Basics.md), to configure the client:
+
+````csharp
+context.Services.AddAuthentication()
+    .AddFacebook(facebook =>
+    {
+        facebook.AppId = "...";
+        facebook.AppSecret = "...";
+        facebook.Scope.Add("email");
+        facebook.Scope.Add("public_profile");
+    });
+````
+
+> It would be a better practice to use the `appsettings.json` or the ASP.NET Core User Secrets system to store your credentials, instead of a hard-coded value like that. Follow the [Microsoft's document](https://docs.microsoft.com/en-us/aspnet/core/security/authentication/social/facebook-logins) to learn the user secrets usage.

docs/en/Startup-Templates/Application.md

@@ -437,7 +437,11 @@ See the [Testing Overview](https://reactjs.org/docs/testing.html) document.
 * [Formik](https://github.com/jaredpalmer/formik) is used to build forms.
 * [Yup](https://github.com/jquense/yup) is used for form validations.
 
+## Social / External Logins
+
+If you want to configure social/external logins for your application, please follow the [Social/External Logins](../Authentication/Social-External-Logins.md) document.
+
 ## What's Next?
 
-- [The getting started document](../Getting-Started-With-Startup-Templates.md) explains how to create a new application in a few minutes.
-- [The application development tutorial](../Tutorials/Part-1) explains step by step application development.
+- [The getting started document](../Getting-Started.md) explains how to create a new application in a few minutes.
+- [The application development tutorial](../Tutorials/Part-1.md) explains step by step application development.

docs/en/docs-nav.json

@@ -107,6 +107,15 @@
       "text": "CLI",
       "path": "CLI.md"
     },
+    {
+      "text": "Authentication",
+      "items": [
+        {
+          "text": "Social/External Logins",
+          "path": "Authentication/Social-External-Logins.md"
+        }
+      ]
+    },
     {
       "text": "Fundamentals",
       "items": [