Credentials being cached between requests to separate remotes with the same URL

The current implementation of ManagedHttpSmartSubtransportStream uses a static CredentialCache. The credentials in this cache are only differentiated by URL and authentication scheme, if you have two separate repositories configured with the same URL, it's possible to authenticate to a repository without providing valid credentials.

Reproduction steps

using System;
using System.Net;
using LibGit2Sharp;

namespace Example
{
    class Program
    {
        static void Main(string[] args)
        {
            var uri = "<repository URL>";

            var repo1 = Repository.Clone(uri, "directory1", new CloneOptions
            {
                BranchName = "main",
                CredentialsProvider = CredentialsHandlerThatReturnsValidCredentials
            }); // This will succeed

            var repo2 = Repository.Clone(uri, "directory2", new CloneOptions
            {
                BranchName = "main",
                CredentialsProvider = CredentialHandlerThatReturnsInvalidCredentials
            }); // Invalid credential provider is never called, cached credentials from the first request are used
        }

        public static Credentials CredentialsHandlerThatReturnsValidCredentials(string url, string usernameFromUrl,
            SupportedCredentialTypes types)
        {
            return new UsernamePasswordCredentials
            {
                Username = "<valid username>",
                Password = "<valid password>"
            };
        }

        public static Credentials CredentialHandlerThatReturnsInvalidCredentials(string url, string usernameFromUrl,
            SupportedCredentialTypes types)
        {
            return new UsernamePasswordCredentials
            {
                Username = "invalid username",
                Password = "invalid password"
            };
        }
    }
}

Expected behavior

Second clone should not authenticate, invalid credentials supplied.

Actual behavior

Authenticates with repository successfully, as there has already been a successful authentication to that repository URL.

Version of LibGit2Sharp (release number or SHA1)

0.27.0-preview-0102

Operating system(s) tested; .NET runtime tested

macOS, .NET 5

从 LibGit2Sharp/Core/ManagedHttpSmartSubtransport.cs 开始，重点检查 ManagedHttpSmartSubtransportStream 使用的静态 CredentialCache。使用相同的 URL 和彼此独立的凭据提供程序复现这两次克隆，然后验证第二个提供程序会被调用，并且无效凭据无法成功完成身份验证。