Added request_access_token and documentation

lib/Facebook/Graph.pm

@@ -71,6 +71,22 @@ sub request_access_token {
     return $token;
 }
 
+sub request_extended_access_token {
+    my ($self, $access_token) = @_;
+
+	die "request_extended_access_token requires an access_token" unless $access_token or $self->has_access_token;
+	$access_token = $access_token ? $access_token : $self->access_token;
+
+    my $token = Facebook::Graph::AccessToken->new(
+        access_token    => $access_token,
+        postback        => $self->postback,
+        secret          => $self->secret,
+        app_id          => $self->app_id,
+    )->request;
+    $self->access_token($token->token);
+    return $token;
+}
+
 sub convert_sessions {
     my ($self, $sessions) = @_;
     return Facebook::Graph::Session->new(
@@ -342,9 +358,17 @@ Handle the Facebook authorization code postback:
  my $q = Plack::Request->new($env);
  $fb->request_access_token($q->query_param('code'));
 
+ #now retrieve extended access token
+ $fb->request_extended_access_token; #extended access token now in $fb->access_token
+
 Or if you already had the access token:
 
  $fb->access_token($token);
+ $fb->request_extended_access_token; 
+
+Or simply:
+
+ $fb->request_extended_access_token($token);
 
 Get some info:
 
@@ -403,6 +427,12 @@ Creates a L<Facebook::Graph::Authorize> object, which can be used to get permiss
 
 Creates a L<Facebook::Graph::AccessToken> object and fetches an access token from Facebook, which will allow everything you do with Facebook::Graph to work within user privileges rather than through the public interface. Returns a L<Facebook::Graph::AccessToken::Response> object, and also sets the C<access_token> property in the Facebook::Graph object.
 
+=head2 request_extended_access_token ( access_token )
+
+Note: access_token is optional. Creates a L<Facebook::Graph::AccessToken> object and fetches an (https://developers.facebook.com/docs/facebook-login/access-tokens/#extending) extended access token from Facebook.
+This method accepts an optional access token. If you have called C<request_access_token> already on the Facebook::Graph object and C<access_token> is set, then you do not have to pass
+in an access token. However, if you have an access token stored from a previous object, you will need to pass it in.
+
 =head3 code
 
 An authorization code string that you should have gotten by going through the C<authorize> process.

lib/Facebook/Graph/AccessToken.pm

@@ -22,19 +22,44 @@ has postback => (
 
 has code => (
     is      => 'ro',
-    required=> 1,
+    required=> 0,
+    predicate=> 'has_code',
+);
+
+has access_token => (
+	is => 'ro',
+	required => 0,
+	predicate => 'has_access_token',
 );
 
+sub BUILD { 
+	my $self = shift;
+	die "Either code or access_token is required" if not $self->has_code and not $self->has_access_token;
+}
+
 sub uri_as_string {
     my ($self) = @_;
     my $uri = $self->uri;
     $uri->path('oauth/access_token');
-    $uri->query_form(
-        client_id       => $self->app_id,
-        client_secret   => $self->secret,
-        redirect_uri    => $self->postback,
-        code            => $self->code,
-    );
+
+	if($self->has_code) {
+		$uri->query_form(
+			client_id       => $self->app_id,
+			client_secret   => $self->secret,
+			redirect_uri    => $self->postback,
+			code            => $self->code,
+		);
+	}
+	else { 
+		$uri->query_form(
+			grant_type 			=> 'fb_exchange_token',
+			client_id       	=> $self->app_id,
+			client_secret   	=> $self->secret,
+			redirect_uri    	=> $self->postback,
+			fb_exchange_token	=> $self->access_token,
+		);
+	}
+
     return $uri->as_string;
 }