I'm trying to use REST API access. I followed all the guides found to enable the api and oauth functionalities.
I'm using this code to retrieve the access and then make the request

    <?php

      class Vashi_Restapi_TestController extends Mage_Core_Controller_Front_Action {
    
        public function indexAction() {

        //Basic parameters that need to be provided for oAuth authentication
        //on Magento

             $params = array(
                'siteUrl' => Mage::getBaseUrl().'/oauth',
                'requestTokenUrl' => Mage::getBaseUrl().'/initiate',
                'accessTokenUrl' => Mage::getBaseUrl().'/oauth/token',
    
                'consumerKey' => '3157bsm22p5q80t7zcujfi9uzxafefic',//Consumer key registered in server administration
                'consumerSecret' => 'zo22y43t1d63okihubfgkg39rdg3pjvl',//Consumer secret registered in server administration
                'callbackUrl' => Mage::getBaseUrl().'/restapi/test/callback',//Url of callback action below
            );
    
            // Initiate oAuth consumer with above parameters
            $consumer = new Zend_Oauth_Consumer($params);
            // Get request token
            $requestToken = $consumer->getRequestToken();
    
            // Get session
            $session = Mage::getSingleton('core/session');
            // Save serialized request token object in session for later use
            $session->setRequestToken(serialize($requestToken));
            // Redirect to authorize URL
            $consumer->redirect();
    
            return;
        }
    
        public function callbackAction() {
    
            //oAuth parameters
            $params = array(
                'siteUrl' => Mage::getBaseUrl().'/oauth',
                'requestTokenUrl' => Mage::getBaseUrl().'/initiate',
                'accessTokenUrl' => Mage::getBaseUrl().'/oauth/token',
                'consumerKey' => '3157bsm22p5q80t7zcujfi9uzxafefic',
                'consumerSecret' => 'zo22y43t1d63okihubfgkg39rdg3pjvl'
            );
    
            // Get session
            $session = Mage::getSingleton('core/session');
            // Read and unserialize request token from session
            $requestToken = unserialize($session->getRequestToken());
            // Initiate oAuth consumer
            $consumer = new Zend_Oauth_Consumer($params);
            // Using oAuth parameters and request Token we got, get access token
            $acessToken = $consumer->getAccessToken($_GET, $requestToken);
            // Get HTTP client from access token object
            $restClient = $acessToken->getHttpClient($params);
            // Set REST resource URL
            $restClient->setUri(Mage::getBaseUrl().'/api/rest/products');
            // In Magento it is neccesary to set json or xml headers in order to work
            $restClient->setHeaders('Accept', 'application/json');
            // Get method
            $restClient->setMethod(Zend_Http_Client::GET);
            //Make REST request
            $response = $restClient->request();
            // Here we can see that response body contains json list of products
            Zend_Debug::dump($response);
    
            return;
        }
    }

I tried also the admin, customers and guest access but the result is always:

    An error occurred. Your authorization request is invalid.

It seems the oauth token is not being generated as the url I can see is:

    http://magentohost/oauth/authorize/?oauth_token=&oauth_callback=http%3A%2F%2Fmagentohost%2F%2Frestapi%2Ftest%2Fcallback

Really struggling with it, any advice?
thanks