<?php
/**
 * @author      Alex Bilbie <hello@alexbilbie.com>
 * @copyright   Copyright (c) Alex Bilbie
 * @license     http://mit-license.org/
 *
 * @link        https://github.com/thephpleague/oauth2-server
 */

namespace League\OAuth2\Server\Entities\Traits;

trait ClientTrait
{
    /**
     * @var string
     */
    protected $name;

    /**
     * @var string|string[]
     */
    protected $redirectUri;

    /**
     * @var bool
     */
    protected $isConfidential;

    /**
     * Get the client's name.
     *
     * @return string
     * @codeCoverageIgnore
     */
    public function getName()
    {
        return $this->name;
    }

    /**
     * Returns the registered redirect URI (as a string).
     *
     * Alternatively return an indexed array of redirect URIs.
     *
     * @return string|string[]
     */
    public function getRedirectUri()
    {
        return $this->redirectUri;
    }

    /**
     * Returns true if the client is confidential.
     *
     * @return bool
     */
    public function isConfidential()
    {
        return $this->isConfidential;
    }
}

<?php
/**
 * @author      Alex Bilbie <hello@alexbilbie.com>
 * @copyright   Copyright (c) Alex Bilbie
 * @license     http://mit-license.org/
 *
 * @link        https://github.com/thephpleague/oauth2-server
 */

namespace League\OAuth2\Server\Entities\Traits;

trait ClientTrait
{
    /**
     * @var string
     */
    protected $name;

    /**
     * @var string|string[]
     */
    protected $redirectUri;

    /**
     * Get the client's name.
     *
     * @return string
     * @codeCoverageIgnore
     */
    public function getName()
    {
        return $this->name;
    }

    /**
     * Returns the registered redirect URI (as a string).
     *
     * Alternatively return an indexed array of redirect URIs.
     *
     * @return string|string[]
     */
    public function getRedirectUri()
    {
        return $this->redirectUri;
    }
}

--- 
+++ 
@@ -22,6 +22,11 @@
     protected $redirectUri;
 
     /**
+     * @var bool
+     */
+    protected $isConfidential;
+
+    /**
      * Get the client's name.
      *
      * @return string
@@ -43,4 +48,14 @@
     {
         return $this->redirectUri;
     }
+
+    /**
+     * Returns true if the client is confidential.
+     *
+     * @return bool
+     */
+    public function isConfidential()
+    {
+        return $this->isConfidential;
+    }
 }
Add isConfidential function to client entity trait
