Question

I want to get FB-user data via the Graph API (with Perl).
I have an facebook-application, configured as “Website with FB Login”.
I’m using Net::Facebook::Oauth2

the app is configured with a callbackurl like this: "http://localhost/myfile.pl"

When I open localhost/myfile.pl it lets me login to facebook and also give the application access to my data. But when it comes to the point where it should fall back and getting the access-token (at least I think thats what it should do next) it ends in an endless loop.

http://localhost/myfile.pl contains the following:

#!"C:\strawberry\perl\bin\perl.exe"
use CGI::Carp qw(fatalsToBrowser);  # this makes perl showing (syntax) errors in browser

use CGI;
    my $cgi = CGI->new;

    use Net::Facebook::Oauth2;

    my $fb = Net::Facebook::Oauth2->new(
        application_id => 'xxxMY_APP_IDXXX', 
        application_secret => 'xxxMY_SECRETxxx',
        callback => 'http://localhost/myFile.pl'
    );

    ###get authorization URL for your application
    my $url = $fb->get_authorization_url(
        scope => ['offline_access','publish_stream'],
        display => 'page'
    );

    ####now redirect to this url
    print $cgi->redirect($url);

    ##once user authorizes your application facebook will send him/her back to your application
    ##to the callback link provided above

    ###in your callback block capture verifier code and get access_token

    my $fb = Net::Facebook::Oauth2->new(
        application_id => 'xxxMY_APP_IDxxx',
        application_secret => 'xxxMY_SECRETxxx',
        callback => 'http://localhost/myFile.pl'
    );

    my $access_token = $fb->get_access_token(code => $cgi->param('code'));
    ###save this token in database or session

    ##later on your application you can use this verifier code to comunicate
    ##with facebook on behalf of this user

    my $fb = Net::Facebook::Oauth2->new(
        access_token => $access_token
    );

    my $info = $fb->get(
        'https://graph.facebook.com/me' ##Facebook API URL
    );

    print $info->as_json;

Am I doing something wrong in the Perl script? Or is it because of the localhost for my callback?

Thanks in advance,
Christoph Twrdy

Answer 1

You should use a parameter to stop infinite loops happen. Basicly, the app authtenticate to FB then call the same script again, it sees that it is authtenticated and loops forever.

if ( ! defined $cgi->param('code') ){
  my $access_token = $fb->get_access_token(code => $cgi->param('code'));
  my $fb = Net::Facebook::Oauth2->new(
    application_id => 'xxxMY_APP_IDxxx',
    application_secret => 'xxxMY_SECRETxxx',
    callback => "http://localhost/myFile.pl";
  );
  ###get authorization URL for your application
  my $url = $fb->get_authorization_url(
    scope => ['offline_access','publish_stream'],
    display => 'page'
  );

  ####now redirect to this url
  print $cgi->redirect($url);

} else {
  ##later on your application you can use this verifier code to comunicate
  ##with facebook on behalf of this user
  my $access_token = $fb->get_access_token(code => $cgi->param('code'));
  my $fb = Net::Facebook::Oauth2->new(
    access_token => $access_token
  );

  my $info = $fb->get(
    'https://graph.facebook.com/me' ##Facebook API URL
  );

  print $info->as_json;
}