title: PHP base64 encoding custom alphabet
body: <p>I try to use base64_encode() and base64_decode() but with custom alphabet. Default alphabet is:</p>
  
  <pre><code>"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
  </code></pre>
  
  <p>say I want to use:</p>
  
  <pre><code>"ZYXWVUTSRQPONMLKJIHGFEDCBAzyxwvutsrqponmlkjihgfedcba9876543210+/" 
  </code></pre>
  
  <p>found a class on internet but doesn't work as expected. Any idea on how to achieve this as simple as possible?</p>