Credential handling in 0.27.0-preview-0096 fails against VSTS/Azure

Between versions preview-0034 and preview-0096 the credential handling changed and no longer works with VSTS/Azure

Include="LibGit2Sharp" Version="0.27.0-preview-0034" - works correctly

Include="LibGit2Sharp" Version="0.27.0-preview-0096" - authentication fails

Reproduction steps

string surl = "https://testsite.visualstudio.com/testsite/_git/Test";
string un = "pat";
string pwd = "";

var credentialsProvider = new CredentialsHandler((_url, _user, _cred) =>
new UsernamePasswordCredentials
{
Username = un,
Password = pwd
}
);

var references = Repository.ListRemoteReferences(surl, credentialsProvider);

Expected behavior

Should return references

Actual behavior

preview-0096 throws "this remote has never connected" error when authentication fails.

Version of LibGit2Sharp (release number or SHA1)

0.27.0-preview-0096

Operating system(s) tested; .NET runtime tested

OSx, .net core 5.0

首先，使用 Repository.ListRemoteReferences、VSTS/Azure URL 和提供的 CredentialsHandler，在 LibGit2Sharp 0.27.0-preview-0034 和 preview-0096 中重现该问题。比较两个版本之间的凭据处理方式；当 preview-0096 的情况能够成功进行身份验证并返回引用，而不是抛出 "this remote has never connected" 时，即表示完成。