[12.x] Add refreshToken relation to Token model (#1739)

* Add refreshToken relation

* Update Token.php

---------

Co-authored-by: Taylor Otwell <taylor@laravel.com>

src/Token.php

@@ -57,6 +57,16 @@ public function client()
         return $this->belongsTo(Passport::clientModel());
     }
 
+    /**
+     * Get the refresh token associated with the token.
+     *
+     * @return \Illuminate\Database\Eloquent\Relations\HasOne
+     */
+    public function refreshToken()
+    {
+        return $this->hasOne(Passport::refreshTokenModel(), 'access_token_id');
+    }
+
     /**
      * Get the user that the token belongs to.
      *