503 - During clone

Version of LibGit2Sharp (release number or SHA1)

Master -7f59d22c

Operating system(s) tested; .NET runtime tested

I receive a "503" when trying to clone a repo from our self host git-service (gitea)

url looks like this:
https://{server}/git/{orga}/{repo}

cloning via git command line works without any problem:
git clone https://mytoken@{server}/git/{orga}/{repo}

i'm passing the token via cloneoptions.Credentialsprovider

 var co = new CloneOptions();
            co.CredentialsProvider = (_url, _user, _cred) =>
                new UsernamePasswordCredentials
                {
                    Username = "mytoken",
                    Password = string.Empty
                };

            string clonedRepoPath = Repository.Clone(url, scd.DirectoryPath, co);

Stacktrace:
LibGit2Sharp.LibGit2SharpException : request failed with status code: 503

   at LibGit2Sharp.Core.Ensure.HandleError(Int32 result) in C:\Users\stefan.kneidl\Source\Repos\libgit2sharp\LibGit2Sharp\Core\Ensure.cs:line 154
   at LibGit2Sharp.Core.Ensure.ZeroResult(Int32 result) in C:\Users\stefan.kneidl\Source\Repos\libgit2sharp\LibGit2Sharp\Core\Ensure.cs:line 172
   at LibGit2Sharp.Core.Proxy.git_clone(String url, String workdir, GitCloneOptions& opts) in C:\Users\stefan.kneidl\Source\Repos\libgit2sharp\LibGit2Sharp\Core\Proxy.cs:line 276
   at LibGit2Sharp.Repository.Clone(String sourceUrl, String workdirPath, CloneOptions options) in C:\Users\stefan.kneidl\Source\Repos\libgit2sharp\LibGit2Sharp\Repository.cs:line 793
   at LibGit2Sharp.Tests.CloneFixture.CanCloneGitea(String url) in C:\Users\stefan.kneidl\Source\Repos\libgit2sharp\LibGit2Sharp.Tests\CloneFixture.cs:line 55

As additional information when trying to access the git server via browser:
https://{myserver}/git
returns: The service is not available. Please try again later.
https://{myserver}/git/ works as intended

Start with LibGit2Sharp.Tests/CloneFixture.cs at CanCloneGitea and trace Repository.Clone through Core/Proxy.cs and Core/Ensure.cs. Compare the failing self-hosted URL and CredentialsProvider with the working command-line clone, including the server's differing /git and /git/ responses. Done means the clone behavior is explained or corrected and covered by a focused regression test.