title: Changes to config variables aren't persisten laravel 5.2
body: <p>I'm having a problem where I need to change a config variable used by oauth2 server based on client-id. This is the configuration:</p>
  
  <pre><code>'grant_types' =&gt; [
          'password' =&gt; [
              'class' =&gt; '\League\OAuth2\Server\Grant\PasswordGrant',
              'callback' =&gt; '\App\Api\OAuth2\PasswordGrantVerifier@verify',
              'access_token_ttl' =&gt; 3600
          ],
  ]
  </code></pre>
  
  <p>Then before i issue a token with <code>Authorizer::issueAccessToken();</code> I set the config variable: <code>config(['oauth2.grant_types.password.access_token_ttl' =&gt; 86400]);</code> if I then run <code>dd(config('oauth2'));</code> I get:</p>
  
  <pre><code>'grant_types' =&gt; array:1 [
          'password' =&gt; array:3 [
              'class' =&gt; '\League\OAuth2\Server\Grant\PasswordGrant',
              'callback' =&gt; '\App\Api\OAuth2\PasswordGrantVerifier@verify',
              'access_token_ttl' =&gt; 86400
          ],
  ]
  </code></pre>
  
  <p>But if I let the code run and issue the token the response is still: </p>
  
  <pre><code>{
      "access_token": "HOoODcDzXilakd5TtOv4qqBSBUwEqqWhIL36ALdM",
      "token_type": "Bearer",
      "expires_in": 3600,
      "refresh_token": "6mfyizKlRGC55x6ZY8ROx24UcVeWfljikNZv6ME7",
      "allowed_scopes": [
        "*"
      ],
      "user_is_activated": true
  }
  </code></pre>
  
  <p>If i hardcode the value <code>'access_token_ttl' =&gt; 86400</code> I get the desired result of: </p>
  
  <pre><code>{
      "access_token": "HOoODcDzXilakd5TtOv4qqBSBUwEqqWhIL36ALdM",
      "token_type": "Bearer",
      "expires_in": 86400,
      "refresh_token": "6mfyizKlRGC55x6ZY8ROx24UcVeWfljikNZv6ME7",
      "allowed_scopes": [
        "*"
      ],
      "user_is_activated": true
  }
  </code></pre>
  
  <p>The problem is that <code>access_token_ttl</code> needs to be dynamic based on the client id. I can't make changes to the vendor library because this would break in future updates. Does someone know of a way to change config variables application wide at runtime that still persists in different methods? </p>