我花了一天的时间，试遍了这里的一切。 对我来说，我没有在Visual Studio中更新我的密码!

I had changed my work Microsoft account password last week or so, I also use that account to login to visual studio, however I wasn't prompted to update it and was not logged out of Visual Studio, it remained logged in. When I clicked on my initials in the top right of visual studio > Account settings > under All Accounts the work account had yellow exclamation triangle warning sign next to it, updated the new password, then updated some packages, dotnet restore, cleaned & rebuilt and the errors are gone.

在我的例子中，我只是重新启动docker并工作。

在我的情况下，我失去了与Git的连接。我只是再次添加连接，它工作!：

新包管理器的开发人员在2019年建议禁用tls 1.3作为解决方案(见第7705期)。

通过按Win + R打开注册表编辑器，并键入regedit Enter

导航到:

\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.3\Client

将“DisabledByDefault key 0”的值修改为1

然后重新启动Visual Studio。

在维基百科上阅读更多关于TLS的信息 阅读更多关于问题7705 w.r.t. NuGet在github

第三方编辑

请注意，这将禁用操作系统的tls 1.3，而不仅仅是对nuget或dotnet。 Windows 10 1909版确实包含TLS 1.3的实验性实现，但后续版本应该没问题。基于无法浏览nuget包的一个答案，您可以通过控制台程序测试tls是否存在问题

static async Task Main(string[] args)
{
    var client = new HttpClient();
    string uri = "https://apiint.nugettest.org/v3-index/index.json";
    var response = await client.GetAsync(uri);
    string msg = "If you see this, your machine has no TLS/SSL issues with nuget.org";
    Console.WriteLine(msg);

}

禁用防病毒应用程序。 以我为例，AVG阻止我访问nuget.org

I had the same error message while scaffolding Identity to my ASP.NET Core MVC project. Since my connection was not behind a proxy, removing/editing proxy configurations didn't make sense. And I didn't want to delete a file or uninstall PMC either. While looking around I realized a "Clear All Nuget Cache(s)" button on Tools --> Options --> NuGet Package Manager --> General. After pressing the button I had to wait for some time for the operation to complete. After that I tried to scaffold the Identity again but it didn't work. Then I decided to restart VS and voila :)