For all sub-sequence API calls, you just need to pass the token without username in base64 encode to the request header. So something like this:  string authToken = @":token"; authToken = Convert.ToBase64String(Encoding.Default.GetBytes(authToken));  (I'm not C# expert)
I build ScaleIO REST Client. I succeed  login using "/api/login"parameter,and the login returns token(key) "xxxxx" . ↓ C# code "HTTP Basic authentication" -- string authInfo = @"admin:password"; authInfo = Convert.ToBase64String(Encoding.Default.GetBytes(authInfo)); request.Headers["Authorization"] = "Basic " + authInfo; --  but,I don't know use token(key) "xxxxx". For example,when I  invoke  HTTP GET request using "/api/instances/"parameter, returns authentication erorr(401) at System.Net.WebException.  C# code --  reqest.Headers["-Auth-Tken"] = "xxxxx";  // "xxxxx" is access_token. --
How to use REST API