Facebook C# SDK Post to Page as Page

Question

I have been struggling to get the Facebook C# SDK to post to my page, as the page for a couple of days.

From my googling, I have found that the process should be as follows:

1. Authorize application for manage_pages and publish_stream with my user account (done through this URL: https://graph.facebook.com/oauth/authorize?client_id=CLIENT_ID&redirect_uri=REDIRECT_URI&scope=publish_stream,manage_pages)
2. Get user access token
3. Exchange user access token for long lived access token
4. Get me/accounts with the long lived user access token
5. Get the page access token from the result
6. Post to the page_id/feeds endpoint using the long lived token

I can follow this process through the graph explorer, and it works. A post is created on the page with the generated token.

How do I do this using the C# SDK?

I tried:

dynamic userTokenResult = client.Get("oauth/access_token", new
{
    client_id = appid,
    client_secret = appsecret,
    grant_type = "client_credentials"
});

dynamic longLivedResult = client.Get("oauth/access_token", new
{
    client_id = appid,
    client_secret = appsecret,
    grant_type = "fb_exchange_token",
    fb_exchange_token = userTokenResult.access_token;
});

client.AccessToken = longLivedResult.access_token;

// Post the message
dynamic messagePost = new
{
    link = message.LinkUrl,
    name = message.LinkName,
    caption = message.LinkCaption,
    description = message.LinkDescription,
    message = message.Message
};

// Set the status
var postId = client.Post("pagename/feed", messagePost);

However, I suspect that this is returning the application access_token, not the user access_token (it fails at GET: me/accounts).

Answer 1

you cannot get user token from server-side code (even if you know login/password). You should either:

1. copy/paste it from Graph API Explorer
2. Get it from JS SDK client side

3. Use GetLoginUrl function from FacebookClient to get login URL and redirect the user to that page. After login is completed, facebook will call your function back - and in that function you will be able to the the token. Below are 2 functions (authorize and callback) from my MVC project - but I think you will get the idea.

    public ActionResult Authorize(Guid eventId)
    {
   
   var redirectUri = ConfigurationProvider.HostingEndpoint + this.Url.Action("AuthorizeCallback", new { eventCode = eventId });
   
   var service = new FacebookClient();
   var loginUrl = service.GetLoginUrl(new {
       client_id = ConfigurationProvider.FacebookAppId,
       client_secret = ConfigurationProvider.FacebookAppSecret,
       redirect_uri = redirectUri,
       response_type = "code",
       scope = "manage_pages, publish_actions, user_photos, publish_stream" // Add other permissions as needed
   });
   
   return new RedirectResult(loginUrl.AbsoluteUri, permanent: false);
   }
   

that will redirect user to the Facebook login page. When user enters credentials and presses login, this function will be called (note the code parameter - it will be used to get the token):

public ActionResult AuthorizeCallback(string code, string eventCode)
{

    var redirectUri = ConfigurationProvider.HostingEndpoint + this.Url.Action("AuthorizeCallback", new { eventCode = eventId });

    var fb = new FacebookClient();
    dynamic result = fb.Post("oauth/access_token", new
    {
        client_id = ConfigurationProvider.FacebookAppId,
        client_secret = ConfigurationProvider.FacebookAppSecret,
        redirect_uri = redirectUri,
        code = code
    });

    var accessToken = result.access_token;

    // update the facebook client with the access token so 
    // we can make requests on behalf of the user
    fb.AccessToken = accessToken;

    // now get externded app Token
    dynamic extendedToken = fb.Get("oauth/access_token", new
    {
        client_id = ConfigurationProvider.FacebookAppId,
        client_secret = ConfigurationProvider.FacebookAppSecret,
        grant_type = "fb_exchange_token",
        fb_exchange_token = fb.AccessToken
    });


    // Get the user's information
    dynamic me = fb.Get("me");
}

After that you should call "/me/accounts", find your page and get its token from there.