Method for get base URI How can I improve the following code?

private const string OAuthTokenUri = "oauth2/token";

private static string GetOAuthTokenUri(string uriAddress)
{
   var uri = new Uri(uriAddress);
   var baseUri = uri.GetLeftPart(UriPartial.Authority);
   var s = new Uri(new Uri(baseUri), OAuthTokenUri);
   return s.ToString();
}


I call GetOAuthTokenUri() like:

var oauthTokenUri = GetOAuthTokenUri("http://www.example.com/mypage/default.aspx");


As a result I'm getting

http://www.example.com/oauth2/token


Please help to improve GetOAuthTokenUri
Maybe you can do it like this:

private const string OAuthTokenUri = "/oauth2/token";

private static string GetOAuthTokenUri(string uriAddress)
{
   Uri result = null;
   return Uri.TryCreate(new Uri(uriAddress), OAuthTokenUri, out result) ? result.ToString() : string.Empty;
}


Please note the slash I have added to OAuthTokenUri.