Asp.Net WebApi - 在startup.auth.cs中使用PublicClientId有什么用

Question

我是mvc的新手。我尝试制作webapi所以我已经启动了一个webapi项目。我在我的Startup.Auth.cs文件中找到了一个变量：

    public static string PublicClientId { get; private set; }

它也被用于以下功能：

public void ConfigureAuth(IAppBuilder app)
        {
            // Configure the db context and user manager to use a single instance per request
            app.CreatePerOwinContext(ApplicationDbContext.Create);
            app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create);

        // Enable the application to use a cookie to store information for the signed in user
        // and to use a cookie to temporarily store information about a user logging in with a third party login provider
        app.UseCookieAuthentication(new CookieAuthenticationOptions());
        app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie);

        // Configure the application for OAuth based flow
        PublicClientId = "self";
        OAuthOptions = new OAuthAuthorizationServerOptions
        {
            TokenEndpointPath = new PathString("/Token"),
            Provider = new ApplicationOAuthProvider(PublicClientId),
            AuthorizeEndpointPath =
             new PathString("/api/Account/ExternalLogin"),
            AccessTokenExpireTimeSpan = TimeSpan.FromDays(365),
            // In production mode set AllowInsecureHttp = false
            AllowInsecureHttp = true
        };

}

但我无法理解它使用的目的。 我还在以下方法的Accounts Countroller中找到了这个变量的引用。

                // GET api/Account/ExternalLogins?returnUrl=%2F&generateState=true
    [AllowAnonymous]
    [Route("ExternalLogins")]
    public IEnumerable<ExternalLoginViewModel> GetExternalLogins(string returnUrl, bool generateState = false)
    {
        IEnumerable<AuthenticationDescription> descriptions = Authentication.GetExternalAuthenticationTypes();
        List<ExternalLoginViewModel> logins = new List<ExternalLoginViewModel>();

        string state;

        if (generateState)
        {
            const int strengthInBits = 256;
            state = RandomOAuthStateGenerator.Generate(strengthInBits);
        }
        else
        {
            state = null;
        }

        foreach (AuthenticationDescription description in descriptions)
        {
            ExternalLoginViewModel login = new ExternalLoginViewModel
            {
                Name = description.Caption,
                Url = Url.Route("ExternalLogin", new
                {
                    provider = description.AuthenticationType,
                    response_type = "token",
                    client_id = Startup.PublicClientId,
                    redirect_uri = new Uri(Request.RequestUri, returnUrl).AbsoluteUri,
                    state = state
                }),
                State = state
            };
            logins.Add(login);
        }

        return logins;
    }

提前致谢..