向WebAPI身份验证发出请求时，没有“ Access-Control-Allow-Origin”标头出现错误-

Question

我正在尝试通过向后端WebAPI发出请求来从Angular8应用程序对用户进行身份验证。我已经添加并配置了CORS以接受来自localhost：4200 [启动我的Angular应用程序的URL]的请求。

现在，当我单击“登录”时，控制台错误-

Access to XMLHttpRequest at 'http://localhost:33428/token' from origin 'http://localhost:4200' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. 

/ token端点应该来自此-

[EnableCors(origins: "http://localhost:4200", headers: "*", methods: "*")]
    public class ApplicationOAuthProvider : OAuthAuthorizationServerProvider
    {

        public override async Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
        {
            context.Validated();
        }

        public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
        {
            var userStore = new UserStore<ApplicationUser>(new ApplicationDbContext());
            var manager = new UserManager<ApplicationUser>(userStore);
            var user = await manager.FindAsync(context.UserName, context.Password);
            if (user != null)
            {
                var identity = new ClaimsIdentity(context.Options.AuthenticationType);
                identity.AddClaim(new Claim("Username", user.UserName));
                identity.AddClaim(new Claim("Email", user.Email));
                identity.AddClaim(new Claim("FirstName", user.FirstName));
                identity.AddClaim(new Claim("LastName", user.LastName));
                identity.AddClaim(new Claim("LoggedOn", DateTime.Now.ToString()));
                var userRoles = manager.GetRoles(user.Id);
                foreach (string roleName in userRoles)
                {
                    identity.AddClaim(new Claim(ClaimTypes.Role, roleName));
                }
                var additionalData = new AuthenticationProperties(new Dictionary<string, string>{
                    {
                        "role", Newtonsoft.Json.JsonConvert.SerializeObject(userRoles)
                    }
                });
                var token = new AuthenticationTicket(identity, additionalData);
                context.Validated(token);
            }
            else
                return;
        }

        public override Task TokenEndpoint(OAuthTokenEndpointContext context)
        {
            foreach (KeyValuePair<string, string> property in context.Properties.Dictionary)
            {
                context.AdditionalResponseParameters.Add(property.Key, property.Value);
            }

            return Task.FromResult<object>(null);
        }
    }

所以我添加了我的startup.cs文件-

[EnableCors(origins: "http://localhost:4200", headers: "*", methods: "*")]
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            // For more information on how to configure your application, visit http://go.microsoft.com/fwlink/?LinkID=316888

            app.UseCors(CorsOptions.AllowAll);

            OAuthAuthorizationServerOptions option = new OAuthAuthorizationServerOptions
            {
                TokenEndpointPath = new PathString("/token"),
                Provider = new ApplicationOAuthProvider(),
                AccessTokenExpireTimeSpan = TimeSpan.FromMinutes(60),
                AllowInsecureHttp = true
            };
            app.UseOAuthAuthorizationServer(option);
            app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());
        }
    }

这是我的认证角度方法-

userAuthentication(userName, password) {
    var data = "username=" + userName + "&password=" + password + "&grant_type=password";
    var reqHeader = new HttpHeaders({ 'Content-Type': 'application/x-www-urlencoded', 'No-Auth': 'True' });
    return this.http.post(this.rootUrl + '/token', data, { headers: reqHeader });
  }

应该击中http://localhost:33428/token。但是没有。

因此 http://localhost:33428/token 基本上意味着处理将转到 ApplicationOAuthProvider 。不是吗？

那么为什么有人不能告诉我它没有达到我的断点呢？我还需要在哪里配置CORS？这是怎么回事我允许所有操作，在EnableCors中明确提及传入的url等。

请帮助我了解并解决此问题。现在与之抗争三天。