无法使用REST API访问VST中的我的repos

 public class VSTSController : ApiController
{
    const String c_collectionUri = "https://****.visualstudio.com/DefaultCollection";
    const String c_projectName = "****";
    const String c_repoName = "****";

    [HttpGet]
    [Route("api/VSTS/Init")]
    public string Init()
    {

        // Interactively ask the user for credentials, caching them so the user isn't constantly prompted
        VssCredentials creds = new VssClientCredentials();
        creds.Storage = new VssClientCredentialStorage();

        // Connect to VSTS
        VssConnection connection = new VssConnection(new Uri(c_collectionUri), creds);

        // Get a GitHttpClient to talk to the Git endpoints
        GitHttpClient gitClient = connection.GetClient<GitHttpClient>();

        // Get data about a specific repository
        var repo = gitClient.GetRepositoryAsync(c_projectName, c_repoName).Result;
        return repo.RemoteUrl;
    }
}

当我运行这段代码时,我得到一个异常 Microsoft.VisualStudio.Services.Common.VssUnauthorizedException' occurred in mscorlib.dll but was not handled in user code . 如何对VSTS REST API进行身份验证?我听不懂 documentation