Pinterest Authentication in xamarin froms

Can anyone help me for tumblr Authentication in xamarin froms.I try to something like:
var auth = new OAuth2Authenticator
(
clientId: "1442181",
scope: "read", // read_write
authorizeUrl: new System.Uri("https://pinterest.com/oauth/authorize/"),
redirectUrl: new System.Uri("https://www.socialphoto.com")
);