Exchanging external Tokens (Google, Twitter, Facebook,LinkedIn) with IdentityServer access tokens using an extension grant

Supported providers

• Facebook
• LinkedIn
• Twitter
• Google
• GitHub

How to exchange external tokens for IdentityServer access token ?

• Request authentication using the provider's native library.
• Exchange external token with IdentityServer token by making following request to IdentityServer.

POST connect/token
     
     client_id = [your_client_id]
     client_secret = [your_client_secret]
     scopes = [your_scopes]
     grant_type = external
     provider = facebook 
     external_token  = [facebook_access_token]

• If user is already registered then IdentityServer will return the access token, otherwise it will send the user's data and prompt for an email parameter to be added, in this case make another request with an extra email parameter.

POST connect/token
    
    client_id = [your_client_id]
    client_secret = [your_client_secret]
    scopes = [your_scopes]
    grant_type = external
    provider = facebook 
    email = [email protected]
    external_token  = [facebook_access_token]

You can change provider to Facebook , Google , Twitter and LinkedIn and provide respective token in the external_token parameter.

How to setup an external provider

1. Derive an interface from IExternalAuthProvider

public interface IMyCustomProvider : IExternalAuthProvider {
    Provider provider {get;}
}

2. Add your provider to ProviderType enum

public enum ProviderType {
  
  Facebook,
  Twitter,
  Google,
  MyCustomProvider
}

3. Add provider info to ProviderDataSource

 public class ProviderDataSource
    {
        public static IEnumerable<Provider> GetProviders()
        {
            return new List<Provider>
            {
                new Provider
                {
                    ProviderId = 1,
                    Name = "Facebook",
                    UserInfoEndPoint = "https://graph.facebook.com/v2.8/me"
                },
                new Provider
                {
                    ProviderId = 2,
                    Name = "Google",
                    UserInfoEndPoint = "https://www.googleapis.com/oauth2/v2/userinfo"
                },
                 new Provider
                {
                    ProviderId = 3,
                    Name = "Twitter",
                    UserInfoEndPoint = "https://api.twitter.com/1.1/account/verify_credentials.json"
                },
                new Provider 
                {
                    ProviderId = 4,
                    Name="MyCustomProvider",
                    UserInfoEndPoint = "[url to end point which validates the token and returns user data]"
                }
            };
        }
    }

4. Provide an implementation for IMyCustomProvider

public class MyCustomProvider : IMyCustomProvider {

private readonly HttpClient _httpClient;
public MyCustomProvider(HttpClient httpClient) {
  _httpClient = httpClient;
}

public Provider =>_providerRepository.Get()
                                    .FirstOrDefault(x => x.Name.ToLower() == ProviderType.MyCustomProvider.ToString().ToLower());
                                    
public JObject GetUserInfo(string accessToken) {

 var query = "[build your request according to your providers configuration]";
 
 var result = _httpClient.GetAsync(Provider.UserInfoEndPoint + query).Result;
            if (result.IsSuccessStatusCode)
            {
                var infoObject = JObject.Parse(result.Content.ReadAsStringAsync().Result);
                return infoObject;
            }
            return null;

}
}

5. Bind IMyCustomProvider in ServiceCollectionExtensions

 public static IServiceCollection AddProviders(this IServiceCollection services)
        {
            services.AddTransient<IFacebookAuthProvider, FacebookAuthProvider>();
            services.AddTransient<ITwitterAuthProvider, TwitterAuthProvider>();
            services.AddTransient<IGoogleAuthProvider, GoogleAuthProvider>();
            services.AddTransient<IMyCustomProvider,MyCustomProvider>();
            return services;
        }

6. Add MyCustomProvider to ExternalAuthenticationGrant

  providers = new Dictionary<ProviderType, IExternalAuthProvider>();
            providers.Add(ProviderType.Facebook, _facebookAuthProvider);
            providers.Add(ProviderType.Google, _googleAuthProvider);
            providers.Add(ProviderType.Twitter, _twitterAuthProvider);
            providers.Add(ProviderType.LinkedIn, _linkedAuthProvider);
            providers.Add(ProviderType.MyCustomProvider, _myCustomProvider);

7. Make a request to IdentityServer using new provider

POST connect/token
     
     client_id = [your_client_id]
     client_secret = [your_client_secret]
     scopes = [your_scopes]
     grant_type = external
     provider = mycustomprovider 
     external_token  = [access_token_from_custom_provider]