可以使用ASP.NET Core Identity来实现同时使用OAuth和证书认证。具体实现步骤如下：

1. 添加依赖项：在项目的.csproj文件中添加如下依赖项：

2. 配置OAuth授权：在Startup.ConfigureServices方法中添加如下代码：

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:SecretKey"]))
        };
    });

3. 配置证书认证：在Startup.ConfigureServices方法中添加如下代码：

services.AddAuthentication("CertificateAuthentication")
    .AddCertificate(options =>
    {
        options.RevocationMode = X509RevocationMode.NoCheck;
    });

services.AddAuthorization(options =>
{
    options.AddPolicy("CertificatePolicy", policy =>
    {
        policy.AuthenticationSchemes.Add("CertificateAuthentication");
        policy.RequireAuthenticatedUser();
    });
});

4. 配置Identity：在Startup.ConfigureServices方法中添加如下代码：

services.AddIdentity()
    .AddEntityFrameworkStores()
    .AddDefaultTokenProviders();

5. 使用OAuth和证书认证：在需要进行认证的控制器或方法上添加如下代码：

[Authorize(AuthenticationSchemes = JwtBearerDefaults.AuthenticationScheme + ",CertificateAuthentication", Policy = "CertificatePolicy")]
public IActionResult SecureAction()
{
    // 认证通过后执行的方法
}

6. 发送证书：客