是的，假设您使用的是Microsoft.Identity.Web，那么您的登录链接将不会转到/MicrosoftIdentity/Account/SignIn，而是转到您创建的自定义操作，该操作将填充您要使用的策略名称，例如/Account/SignIn：

[AllowAnonymous]
public class AccountController : Controller
{
    public IActionResult SignIn(string? policy)
    {
        var properties = new AuthenticationProperties
        {
            RedirectUri = this.Url.Content("~/"),
        };

        // in this example we're allowing the policy name to be passed in as a parameter to the action, but this would be replaced by your custom policy selection logic
        if (!string.IsNullOrWhiteSpace(policy))
        {
            properties.Items["policy"] = policy;

            // HACK: Microsoft.Identity.Web removes the policy item as part of the redirect to IdP but we need to update the token URL when using code flow, so fix that...
            properties.Items["customPolicy"] = policy;
        }

        return this.Challenge(properties, OpenIdConnectDefaults.AuthenticationScheme);
    }
}

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通过填充AuthenticationProperties.Items["policy"]，Microsoft.Identity.Web在重定向到B2C /authorize端点时将自动使用该策略名称。但是，如果您正在使用OpenID Connect code流（您应该这样做），则需要确保/token端点也使用正确的策略。
Microsoft.Identity.Web在/authorize调用之后删除policy项，因此上面的示例还将策略名称设置为customPolicy，以便在需要交换令牌时可用。只需更新Startup.cs中的Microsoft.Identity.Web配置，即可处理OnAuthorizationCodeReceived事件：

services.AddAuthentication(OpenIdConnectDefaults.AuthenticationScheme)
        .AddMicrosoftIdentityWebApp(opt =>
        {
            // other setup here...

            opt.Events.OnAuthorizationCodeReceived += ctx =>
            {
                if (ctx.Properties?.Items.TryGetValue("customPolicy", out var customPolicy) == true)
                {
                    ctx.TokenEndpointRequest.TokenEndpoint = $"{opt.Instance}/{opt.Domain}/{customPolicy}/oauth2/v2.0/token";
                }

                return Task.CompletedTask;
            };
        }/* cookie config happens here if you're overriding defaults */);

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如果你想让[Authorize]正常工作，你还需要更改默认的身份验证方案，以便它检查你的cookie并更新cookie配置，使用你的自定义登录URL而不是默认的Microsoft.Identity.Web URL：

services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
        .AddMicrosoftIdentityWebApp(opt =>
        {
            // other setup here...

            opt.Events.OnAuthorizationCodeReceived += ctx =>
            {
                if (ctx.Properties?.Items.TryGetValue("customPolicy", out var customPolicy) == true)
                {
                    ctx.TokenEndpointRequest.TokenEndpoint = $"{opt.Instance}/{opt.Domain}/{customPolicy}/oauth2/v2.0/token";
                }

                return Task.CompletedTask;
            };
        },
        opt =>
        {
            // this should be the actual URL, not just the controller and action name
            opt.LoginPath = "/Account/SignIn";
            opt.Cookie.SameSite = SameSiteMode.None;
            opt.Cookie.SecurePolicy = CookieSecurePolicy.Always;
            opt.Cookie.IsEssential = true;
        });

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