Idsv4是不关心客户端是谁的，我有一些想法，不知道是不是你需要的。
首先在Core的IdentityServer4上自定义登录地址。

services.AddIdentityServer(options =>
            {
                   // 忽略
                options.UserInteraction.LoginUrl = Configuration["ApplicationDTO:LoginUrl"]; // 假设是/users/signIn
                options.UserInteraction.LogoutUrl = Configuration["ApplicationDTO:LogoutUrl"]; /
            })

新建一个UsersControllers.添加signIn的Action.

[HttpGet]
        [Authorize(AuthenticationSchemes = CookieAuthenticationDefaults.AuthenticationScheme)]
        public async Task<IActionResult> SignIn(string returnUrl)
        {
            //通过验证后即清除cookies
            await HttpContext.SignOutAsync("Cookies");

            #region Issued Cookie

            List<Claim> source = new List<Claim>()
            {
                new Claim("sub",new Guid().ToString()),
                new Claim("name",User.Identity.Name),
                new Claim("idp", "xxxxx"),
                new Claim("role","Custom"),
                new Claim("auth_time", DateTimeOffset.Now.ToEpochTime().ToString(),"http://www.w3.org/2001/XMLSchema#integer")
            };
            source.Add(new Claim("amr", "authorization_code"));
            var identity = new ClaimsIdentity(source.Distinct<Claim>((IEqualityComparer<Claim>)new ClaimComparer()), "IdentityServer4", "name", "role");
            var claimsPrincipal = new ClaimsPrincipal(identity);
            await HttpContext.SignInAsync(IdentityServerConstants.DefaultCookieAuthenticationScheme, claimsPrincipal, new AuthenticationProperties
            {
                IsPersistent = true,
                ExpiresUtc = DateTimeOffset.Now.Add(TimeSpan.FromMinutes(43200))
            });

            #endregion
            return Redirect(returnUrl);
        }

Authorize需要您在startup自己定义登录地址。
那么流程就是如下这样的
1.在浏览器访问idsv4服务端https://Coreidsv4/connect/authorize?......，会跳转到/users/login通过Authorize验证用户是否登录，如果未登录就通过Authorization配置的登录地址去登录。登录成功重定向回来。可以在users/login中填写自己要信息。继续下去，通过url获取授权码 code。然后再去拿code去换取token.注意参数填写正确。