// 在登录/认证时添加声明
var claims = new List<Claim>
{
    new Claim(ClaimTypes.Name, user.Username),
    new Claim(ClaimTypes.Email, user.Email),
    new Claim("CustomClaim", "CustomValue"),
    new Claim(ClaimTypes.Role, "Admin")
};

var claimsIdentity = new ClaimsIdentity(claims, "CustomAuthType");
var principal = new ClaimsPrincipal(claimsIdentity);

await HttpContext.SignInAsync(principal);

public class CustomClaimsMiddleware
{
    private readonly RequestDelegate _next;

    public CustomClaimsMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        if (context.User.Identity.IsAuthenticated)
        {
            var identity = (ClaimsIdentity)context.User.Identity;
            identity.AddClaim(new Claim("MiddlewareAdded", DateTime.Now.ToString()));
        }
        
        await _next(context);
    }
}

services.AddAuthorization(options =>
{
    options.AddPolicy("CustomPolicy", policy =>
    {
        policy.RequireAuthenticatedUser();
        policy.RequireClaim("Department", "IT");
        policy.Requirements.Add(new CustomRequirement());
    });
});

public class CustomRequirement : IAuthorizationRequirement
{
    // 自定义需求逻辑
}

public class CustomRequirementHandler : AuthorizationHandler<CustomRequirement>
{
    protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, CustomRequirement requirement)
    {
        // 在此添加声明
        context.User.Identities.First().AddClaim(new Claim("CustomRequirement", "Passed"));
        context.Succeed(requirement);
        return Task.CompletedTask;
    }
}