servicestack and facebook canvas app authentication - facebook

Question

the facebook canvas app gets a "signed_request" parameter when user visits the canvas url via facebook.
How do i use this to authenticate the user on servicestack, so that i get the user session in servicestack.
the user will already be signed up for the app and will have records in the servicestack user repositories.
Should i set the canvas url to /auth/facebook ? with additional ?Continue=/target_url
Will this authenticate the user and send him to the target_url?
Or should i handle the canvas request and then use AuthService to authenticate the user using the "signed_request" param? if this is the case then, how do i proceed with it ?

Answer 1

Here's how I managed the case:
I handled the FB canvas request, receiving the "signed_request" parameter. Then by decoding the BASE64 encoded string (and verifying with HMAC SHA256), I got the FB userId.
if (isMatch)
{
string message = UTF8Encoding.UTF8.GetString(msg);
var output = message.FromJson<Dictionary<string, string>>();
string user = output["user_id"];
OAuthTokens tokens = new OAuthTokens();
tokens.Provider = "facebook";
tokens.UserId = user;
UserSession.IsAuthenticated = true;
((FacebookAuthProvider)AuthService.GetAuthProvider("facebook")).OnAuthenticated(this, UserSession, tokens, new Dictionary<string, string>());
return UserSession.ToJson();
}
I'm not sure whether this is the best way to manually get the user authenticated. But so far, this technique has worked.