title: Laravel:Error when Implementing JWT authentication
body: <p>I am experiencing an error when trying to post the API through Postman to authenticate users in the site.</p>
  
  <p>login function:</p>
  
  <pre><code>    public function login(Request $request)
      {
  
       $credentials = $request-&gt;only('email', 'password');
  
       if ($token = $this-&gt;guard()-&gt;attempt($credentials)) {
          return $this-&gt;respondWithToken($token);
       }
       return response()-&gt;json(['error' =&gt; 'Unauthorized'], 401);
  
    }
  </code></pre>
  
  <p>the guard function</p>
  
  <pre><code>  public function guard()
    {
     return Auth::guard();
    }
  </code></pre>
  
  <p>The error shown on postman</p>
  
  <pre><code>"message": "Call to undefined method Tymon\\JWTAuth\\Contracts\\Providers\\Auth::guard()",
  "exception": "Symfony\\Component\\Debug\\Exception\\FatalThrowableError",
  </code></pre>
  
  <p>How to solve this?</p>