diff --git a/init.php b/init.php
index af5668d..a24fe11 100644
--- a/init.php
+++ b/init.php
@@ -19,7 +19,7 @@ function initDatabase() {
 			clientData TEXT NOT NULL
 		    )',
 		    'CREATE TABLE IF NOT EXISTS allowedClients (
-			userId VARCHAR(255) NOT NULL PRIMARY KEY,
+			userId VARCHAR(255) NOT NULL,
 			clientId VARCHAR(255) NOT NULL
 		    )',
 		    'CREATE TABLE IF NOT EXISTS userStorage (
diff --git a/lib/Routes/SolidIdp.php b/lib/Routes/SolidIdp.php
index 6cc3225..83316a6 100644
--- a/lib/Routes/SolidIdp.php
+++ b/lib/Routes/SolidIdp.php
@@ -120,11 +120,12 @@ public static function respondToRegister() {
 
 
 			$generatedClientId = bin2hex(random_bytes(16)); // 32 chars for the client Id
-			$generatedClientSecret = bin2hex(random_bytes(32)); // and 64 chars for the client secret
-
 			$clientData['client_id_issued_at'] = time();
 			$clientData['client_id'] = $generatedClientId;
-			$clientData['client_secret'] = $generatedClientSecret;
+			if ($clientData['token_endpoint_auth_method'] !== 'none') { // generate and use secret if we have token endpoint authentication
+				$generatedClientSecret = bin2hex(random_bytes(32)); // and 64 chars for the client secret
+				$clientData['client_secret'] = $generatedClientSecret;
+			}
 			$clientData['origin'] = $origin;
 			ClientRegistration::saveClientRegistration($clientData);
 			
@@ -133,16 +134,21 @@ public static function respondToRegister() {
 			$responseData = array(
 				'redirect_uris' => $client['redirect_uris'],
 				'client_id' => $client['client_id'],
-				'client_secret' => $client['client_secret'],
 				'response_types' => array('code'),
 				'grant_types' => array('authorization_code', 'refresh_token'),
 				'application_type' => $client['application_type'] ?? 'web',
 				'client_name' => $client['client_name'] ?? $client['client_id'],
 				'id_token_signed_response_alg' => 'RS256',
-				'token_endpoint_auth_method' => 'client_secret_basic',
-				'client_id_issued_at' => $client['client_id_issued_at'],
-				'client_secret_expires_at' => 0
+				'client_id_issued_at' => $client['client_id_issued_at']
 			);
+			if (isset($client['client_secret'])) {
+				$responseData['client_secret'] = $client['client_secret'];
+				$responseData['token_endpoint_auth_method'] = 'client_secret_basic';
+				$responseData['client_secret_expires_at'] = 0;
+			} else {
+				$responseData['token_endpoint_auth_method'] = 'none'; // No client secret means we can't authenticate on the token endpoint;
+			}
+
 			header("HTTP/1.1 201 Created");
 			header("Content-type: application/json");
 			echo json_encode($responseData, JSON_PRETTY_PRINT | JSON_THROW_ON_ERROR);
diff --git a/lib/Server.php b/lib/Server.php
index ab128a8..80882b5 100644
--- a/lib/Server.php
+++ b/lib/Server.php
@@ -67,6 +67,13 @@ public static function getConfigClient() {
 				$registeredClient = ClientRegistration::getRegistration($clientId);
 			}
 			if (isset($registeredClient)) {
+				/*
+					If the token_endpoint_auth_method is 'none', this means we are dealing with a public client that is not able to securely store the client secret.
+					In that case, we remove the client_secret so we treat the client as a public client
+				*/
+				if ($registeredClient['token_endpoint_auth_method'] === "none") {
+					unset($registeredClient['client_secret']);
+				}
 				return new ConfigClient(
 					$clientId,
 					$registeredClient['client_secret'] ?? '',
diff --git a/upgrade/0.4.1/upgrade.php b/upgrade/0.4.1/upgrade.php
new file mode 100644
index 0000000..c00f8ee
--- /dev/null
+++ b/upgrade/0.4.1/upgrade.php
@@ -0,0 +1,28 @@
+<?php
+        require_once(__DIR__ . "/../../config.php");
+        require_once(__DIR__ . "/../../vendor/autoload.php");
+        
+        use Pdsinterop\PhpSolid\Server;
+
+        function upgradeDatabase() {
+                $statements = [
+                        'BEGIN TRANSACTION',
+                        'CREATE TABLE allowedClients_new (userId VARCHAR(255) NOT NULL, clientId VARCHAR(255) NOT NULL)',
+                        'INSERT INTO allowedClients_new (userId, clientId) SELECT userId, clientId FROM allowedClients',
+                        'DROP TABLE allowedClients',
+                        'ALTER TABLE allowedClients_new RENAME TO allowedClients',
+                        'COMMIT'
+                ];
+                      
+                try {
+                    $pdo = new \PDO("sqlite:" . DBPATH);
+
+                    // create tables
+                    foreach($statements as $statement){
+                        $pdo->exec($statement);
+                    }
+                } catch(\PDOException $e) {
+                    echo $e->getMessage();
+                }
+        }
+        upgradeDatabase();