This tutorial demonstrates how to build an ASP.NET Core 2.x app that enables users to log in using OAuth 2.0 with credentials from external authentication providers.
[Facebook](facebook-logins.md), [Twitter](twitter-logins.md), [Google](google-logins.md), and [Microsoft](microsoft-logins.md) providers are covered in the following sections. Other providers are available in third-party packages such as [AspNet.Security.OAuth.Providers](https://github.com/aspnet-contrib/AspNet.Security.OAuth.Providers) and [AspNet.Security.OpenId.Providers](https://github.com/aspnet-contrib/AspNet.Security.OpenId.Providers).
Enabling users to sign in with their existing credentials is convenient for the users and shifts many of the complexities of managing the sign-in process onto a third party. For examples of how social logins can drive traffic and customer conversions, see case studies by [Facebook](https://www.facebook.com/unsupportedbrowser) and [Twitter](https://dev.twitter.com/resources/case-studies).
Note: Packages presented here abstract a great deal of complexity of the OAuth authentication flow, but understanding the details may become necessary when troubleshooting. Many resources are available; for example, see [Introduction to OAuth 2](https://www.digitalocean.com/community/tutorials/an-introduction-to-oauth-2) or [Understanding OAuth 2](http://www.bubblecode.net/2016/01/22/understanding-oauth2/). Some issues can be resolved by looking at the [ASP.NET Core source code for the provider packages](https://github.com/aspnet/Security/tree/dev/src).
Note: Projects created using **Web Application** or **Web API** project templates for ASP.NET Core 2.x are automatically configured to enable SSL and launch with https URL if the **Individual User Accounts** option was selected on **Change Authentication dialog** in the project wizard as shown above.
These values are effectively the *user name* and *password* your application uses to access their API, and constitute the "secrets" that can be linked to your application configuration with the help of **Secret Manager** instead of storing them in configuration files directly or hard-coding them.
Follow the steps in [Safe storage of app secrets during development in ASP.NET Core](xref:security/app-secrets) topic so that you can store tokens assigned by each login provider below.
When you register with an external login provider, you don't have a password registered with the app. This alleviates you from creating and remembering a password for the site, but it also makes you dependent on the external login provider. If the external login provider is unavailable, you won't be able to log in to the web site.