下面是一个使用ASP.NET Core身份验证与JWT的代码示例：

1. 在Startup.cs文件中配置身份验证服务：

public void ConfigureServices(IServiceCollection services)
{
    // 配置JWT身份验证
    var jwtSettings = Configuration.GetSection("JwtSettings");
    var key = Encoding.ASCII.GetBytes(jwtSettings.GetValue("SecretKey"));

    services.AddAuthentication(options =>
    {
        options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
        options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
    })
    .AddJwtBearer(options =>
    {
        options.RequireHttpsMetadata = false;
        options.SaveToken = true;
        options.TokenValidationParameters = new TokenValidationParameters
        {
            ValidateIssuerSigningKey = true,
            IssuerSigningKey = new SymmetricSecurityKey(key),
            ValidateIssuer = false,
            ValidateAudience = false
        };
    });

    services.AddControllers();
}

2. 在Configure方法中启用身份验证中间件：

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    // 省略其他配置...

    app.UseAuthentication();

    app.UseRouting();
    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });
}

3. 创建一个控制器来处理身份验证请求：

[ApiController]
[Route("[controller]")]
public class AuthController : ControllerBase
{
    private readonly IConfiguration _configuration;

    public AuthController(IConfiguration configuration)
    {
        _configuration = configuration;
    }

    [HttpPost("login")]
    public IActionResult Login(LoginModel model)
    {
        // 从数据库或其他地方验证用户凭据，如果验证成功则生成JWT Token
        if (IsValidUser(model.Username, model.Password))
        {
            var token = GenerateJwtToken();
            return Ok(new { token });
        }

        return Unauthorized();
    }

    private bool IsValidUser(string username, string password)
    {
        // 验证用户凭据的逻辑
    }

    private string GenerateJwtToken()
    {
        var jwtSettings = _configuration.GetSection("JwtSettings");
        var key = Encoding.ASCII.GetBytes(jwtSettings.GetValue("SecretKey"));

        var tokenHandler = new JwtSecurityTokenHandler();
        var tokenDescriptor = new SecurityTokenDescriptor
        {
            Expires = DateTime.UtcNow.AddHours(1),
            SigningCredentials = new SigningCredentials(new SymmetricSecurityKey(key), SecurityAlgorithms.HmacSha256Signature)
        };

        var token = tokenHandler.CreateToken(tokenDescriptor);
        return tokenHandler.WriteToken(token);
    }
}

4. 在appsettings.json文件中配置JWT设置：

"JwtSettings": {
  "SecretKey": "your-secret-key"
}

以上代码示例演示了使用ASP.NET Core身份验证与JWT的基本原理。你可以根据自己的需求进行进一步调整和扩展。