通常情况下，scheme应该填写在Startup.cs文件的ConfigureServices()方法中所添加的认证方案名称。例如，如果在Startup.cs文件中添加了如下代码：

services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme) .AddJwtBearer(options => { options.TokenValidationParameters = new TokenValidationParameters { ValidateIssuer = true, ValidateAudience = true, ValidateLifetime = true, ValidateIssuerSigningKey = true,

        ValidIssuer = Configuration["JwtIssuer"],
        ValidAudience = Configuration["JwtAudience"],
        IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["JwtSecurityKey"]))
    };
});

则在使用AuthenticationHttpContextExtensions.AuthenticateAsync()时，应该填写“JwtBearer”作为scheme：

var result = await HttpContext.AuthenticateAsync("JwtBearer");

完整示例代码：

services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme) .AddJwtBearer(options => { options.TokenValidationParameters = new TokenValidationParameters { ValidateIssuer = true, ValidateAudience = true, ValidateLifetime = true, ValidateIssuerSigningKey = true,

        ValidIssuer = Configuration["JwtIssuer"],
        ValidAudience = Configuration["JwtAudience"],
        IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["JwtSecurityKey"]))
    };
});

...

[HttpGet] public async Task Authenticate() { var result = await HttpContext.AuthenticateAsync("JwtBearer");

if (result.Succeeded)
{
    var claims = result.Principal.Claims;
    // ...
}
else
{
    // ...
}

}