There are three main types of clients. Official Document For Identity Clients Github link for the Official Identity Sample code

Defining a client for server to server communication

In this scenario no interactive user is present - a service (aka client) wants to communicate with an API (aka scope):

public class Clients
{
    public static IEnumerable<Client> Get()
    {
        return new List<Client>
        {
            new Client
            {
                ClientId = "service.client",
                ClientSecrets = { new Secret("secret".Sha256()) },

                AllowedGrantTypes = GrantTypes.ClientCredentials,
                AllowedScopes = { "api1", "api2.read_only" }
            }
        };
    }
}

Defining browser-based JavaScript client (e.g. SPA) for user authentication and delegated access and API

This client uses the so-called implicit flow to request an identity and access token from JavaScript:

var jsClient = new Client
{
    ClientId = "js",
    ClientName = "JavaScript Client",
    ClientUri = "http://identityserver.io",

    AllowedGrantTypes = GrantTypes.Implicit,
    AllowAccessTokensViaBrowser = true,

    RedirectUris =           { "http://localhost:7017/index.html" },
    PostLogoutRedirectUris = { "http://localhost:7017/index.html" },
    AllowedCorsOrigins =     { "http://localhost:7017" },

    AllowedScopes =
    {
        IdentityServerConstants.StandardScopes.OpenId,
        IdentityServerConstants.StandardScopes.Profile,
        IdentityServerConstants.StandardScopes.Email,

        "api1", "api2.read_only"
    }
};

Defining a server-side web application (e.g. MVC) for user authentication and delegated API access

Interactive server-side (or native desktop/mobile) applications use the hybrid flow. This flow gives you the best security because the access tokens are transmitted via back-channel calls only (and gives you access to refresh tokens):

var mvcClient = new Client
{
    ClientId = "mvc",
    ClientName = "MVC Client",
    ClientUri = "http://identityserver.io",

    AllowedGrantTypes = GrantTypes.Hybrid,
    AllowOfflineAccess = true,
    ClientSecrets = { new Secret("secret".Sha256()) },

    RedirectUris =           { "http://localhost:21402/signin-oidc" },
    PostLogoutRedirectUris = { "http://localhost:21402/" },
    FrontChannelLogoutUri =  "http://localhost:21402/signout-oidc",

    AllowedScopes =
    {
        IdentityServerConstants.StandardScopes.OpenId,
        IdentityServerConstants.StandardScopes.Profile,
        IdentityServerConstants.StandardScopes.Email,

        "api1", "api2.read_only"
    },
};

Defining clients in appsettings.json

The AddInMemoryClients extensions method also supports adding clients from the ASP.NET Core configuration file. This allows you to define static clients directly from the appsettings.json file:

"IdentityServer": {
  "IssuerUri": "urn:sso.company.com",
  "Clients": [
    {
      "Enabled": true,
      "ClientId": "local-dev",
      "ClientName": "Local Development",
      "ClientSecrets": [ { "Value": "<Insert Sha256 hash of the secret encoded as Base64 string>" } ],
      "AllowedGrantTypes": [ "implicit" ],
      "AllowedScopes": [ "openid", "profile" ],
      "RedirectUris": [ "https://localhost:5001/signin-oidc" ],
      "RequireConsent": false
    }
  ]
}

Then pass the configuration section to the AddInMemoryClients method:In Startup.cs

AddInMemoryClients(configuration.GetSection("IdentityServer:Clients"))

Subcategories or detail clients list:

1. Client Credentials:

2. Resource Owner Client

3. JS OIDC Client

4. JS OAuth Client

5. MVC Hybrid Client

6. MVC Implicit Client