Web API 已拒绝为此请求授权

{
"Email": "XXX@qq.com",
"Password": "***",
"ConfirmPassword": "***"
}

private string GetToken(string host)
{

        var client = new RestClient(host);

        var request = new RestRequest("/token", Method.POST);

        request.AddParameter("grant_type", "password");

        request.AddParameter("userName", "用户名");

        request.AddParameter("password", "密码");

        //request.AddHeader("Authorization", Convert.ToBase64String(Encoding.ASCII.GetBytes(clientId + ":" + clientSecret)));

        var response = client.Execute(request);

        var s = JObject.Parse(response.Content)["access_token"].Value<string>();

        return s;

}

// If we already have a bearer token, set the Authorization header.
var token = sessionStorage.getItem(tokenKey);
var headers = {};
if (token) {
    headers.Authorization = ‘Bearer ‘ + token;
}

$.ajax({
    type: ‘GET‘,
    url: ‘api/values/1‘,
    headers: headers
}).done(function (data) {
    self.result(data);
}).fail(showError);