diff --git a/src/OAuth2/Storage/ClientInterface.php b/src/OAuth2/Storage/ClientInterface.php
index d0d7fb7d..bb339ffc 100644
--- a/src/OAuth2/Storage/ClientInterface.php
+++ b/src/OAuth2/Storage/ClientInterface.php
@@ -4,5 +4,44 @@ namespace OAuth2\Storage;
 
 interface ClientInterface
 {
-    
-}
+	/**
+	 * Validate a client
+	 *
+	 * Example SQL query:
+	 *
+	 * <code>
+	 * # Client ID + redirect URI
+	 * SELECT clients.id FROM clients LEFT JOIN client_endpoints ON
+	 *  client_endpoints.client_id = clients.id WHERE clients.id = $clientId AND
+	 *  client_endpoints.redirect_uri = $redirectUri
+	 *
+	 * # Client ID + client secret
+	 * SELECT clients.id FROM clients  WHERE clients.id = $clientId AND
+	 *  clients.secret = $clientSecret
+	 *
+	 * # Client ID + client secret + redirect URI
+	 * SELECT clients.id FROM clients LEFT JOIN client_endpoints ON
+	 *  client_endpoints.client_id = clients.id WHERE clients.id = $clientId AND
+	 *  clients.secret = $clientSecret AND client_endpoints.redirect_uri =
+	 *  $redirectUri
+	 * </code>
+	 *
+	 * Response:
+	 *
+	 * <code>
+	 * Array
+	 * (
+	 *     [client_id] => (string) The client ID
+	 *     [client secret] => (string) The client secret
+	 *     [redirect_uri] => (string) The redirect URI used in this request
+	 *     [name] => (string) The name of the client
+	 * )
+	 * </code>
+	 *
+	 * @param  string     $clientId     The client's ID
+	 * @param  string     $clientSecret The client's secret (default = "null")
+	 * @param  string     $redirectUri  The client's redirect URI (default = "null")
+	 * @return bool|array               Returns false if the validation fails, array on success
+	 */
+    public function get($clientId = null, $clientSecret = null, $redirectUri = null);
+}
\ No newline at end of file