diff --git a/index.js b/index.js
index 438cee7..fec9feb 100644
--- a/index.js
+++ b/index.js
@@ -119,11 +119,11 @@ OAuth2Provider.prototype.oauth = function() {
       });
 
     } else if(req.method == 'POST' && self.options.authorize_uri == uri) {
-      var     client_id = req.query.client_id,
-           redirect_uri = req.query.redirect_uri,
-          response_type = req.query.response_type || 'code',
-                  state = req.query.state,
-              x_user_id = req.query.x_user_id;
+      var     client_id = (req.query.client_id || req.body.client_id),
+           redirect_uri = (req.query.redirect_uri || req.body.redirect_uri),
+          response_type = (req.query.response_type || req.body.response_type) || 'code',
+                  state = (req.query.state || req.body.state),
+              x_user_id = (req.query.x_user_id || req.body.x_user_id);
 
       var url = redirect_uri;