以下是一个使用ASP.NET Core WebApi进行身份验证和授权的示例代码：

首先，需要在Startup.cs文件中进行配置：

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
            .AddJwtBearer(options =>
            {
                options.TokenValidationParameters = new TokenValidationParameters
                {
                    ValidateIssuer = true,
                    ValidateAudience = true,
                    ValidateLifetime = true,
                    ValidateIssuerSigningKey = true,
                    ValidIssuer = Configuration["Jwt:Issuer"],
                    ValidAudience = Configuration["Jwt:Audience"],
                    IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["Jwt:Key"]))
                };
            });

        services.AddAuthorization();

        // 添加其他服务
        services.AddControllers();
    }

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

        app.UseAuthentication();
        app.UseAuthorization();

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

然后，您可以在控制器中使用[Authorize]特性来限制访问：

[Route("api/[controller]")]
[ApiController]
public class HomeController : ControllerBase
{
    [HttpGet]
    [Authorize]
    public IActionResult Get()
    {
        // 执行需要授权的操作
        return Ok("Authenticated");
    }
}

最后，生成和验证JWT令牌的代码示例：

public class TokenController : ControllerBase
{
    private readonly IConfiguration _configuration;

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

    [HttpPost]
    public IActionResult CreateToken()
    {
        var claims = new[]
        {
            new Claim(JwtRegisteredClaimNames.Sub, "your_username"),
            new Claim(JwtRegisteredClaimNames.Email, "your_email"),
            new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString())
        };

        var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_configuration["Jwt:Key"]));
        var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);

        var token = new JwtSecurityToken(
            _configuration["Jwt:Issuer"],
            _configuration["Jwt:Audience"],
            claims,
            expires: DateTime.Now.AddMinutes(30),
            signingCredentials: creds);

        return Ok(new
        {
            token = new JwtSecurityTokenHandler().WriteToken(token)
        });
    }
}

需要在appsettings.json文件中添加以下配置：

"Jwt": {
  "Key": "your_secret_key_here",
  "Issuer": "your_issuer_here",
  "Audience": "your_audience_here"
}

在上述示例中，[Authorize]特性将保护Get()方法，只有经过身份验证的用户才能访问它。CreateToken()方法用于生成包含用户声明的JWT令牌。

请注意，上述示例中的配置和代码是一个基本示例，实际应用中可能需要进行更多的配置和安全性措施。