How to register Authentication Provider for identity in ASP.NET Core 3.1 using a custom service? - asp.net-core

Question

I have an ASP.NET Core 3.1 app that uses Identity to authenticate users. I would like to configure Identity to allow external logins from different providers like Facebook and Twitter.
I have multiple external-login-provider stored in a database. These records can be accessed using IAuthProvider service.
When the app is configured using the ConfigureServices() method, I want to resolve an instance of IAuthProvider to get all available records from the database and then add the needed login-providers.
Below is my code I am struggling on how to resolve IAuthProvider instance while in the ConfigureServices() method. Perhaps there is a better way to configure or defer configure the providers until later but not sure how and where to configure the server.
How can I create an instance of the IAuthProvider and correctly configure the Identity providers?
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<AppDbContext>(options =>
{
options.UseMySql(Configuration.GetConnectionString("MySql"));
});
services.AddScoped<IAuthProvider, AuthProvider>();
// other services
var providers = // Here I somehow need to resolve an instance of IAuthProvider;
AuthenticationBuilder authBuilder = services.AddAuthentication();
foreach (var provider in providers.All())
{
if (provider.Name == ExternalLoginProvider.Facebook)
{
authBuilder.AddFacebook(options =>
{
options.AppId = provider.AppId;
options.AppSecret = provider.Secret;
});
}
if (provider.Name == ExternalLoginProvider.Twitter)
{
authBuilder.AddTwitter(options =>
{
options.ConsumerKey = provider.AppId;
options.ConsumerSecret = provider.Secret;
});
}
// Other providers as needed per the records found in the database
}
}

Answer 1

I see your code has already registered the implementation of IAuthProvider, you can simpply call servcice.GetService() to get an instance of AuthProvider.
I don't get your point of having different authprovider in such a way, according to this document you can add different auth provider in chain like this:
services.AddAuthentication()
.AddMicrosoftAccount(microsoftOptions => { ... })
.AddGoogle(googleOptions => { ... })
.AddTwitter(twitterOptions => { ... })
.AddFacebook(facebookOptions => { ... });
Any reason why adding them seperatly?
Edit:
If you just want to get the instance of IAuthProvider, just try
var serviceProvider = services.BuildServiceProvider();
var provider = serviceProvider.GetService<IAuthProvider>();