title: Converting string in Base64 and HMAC sha1
body: <p>I need help with making a signature in swift 3 with <code>HMAC</code> <code>SHA1</code> for a web request.
  I have an example in Java but really do not know how to do it in swift.</p>
  
  <p>Java formula:</p>
  
  <pre><code>signature = Base64.encode(HMAC_SHA1.digest(data,Base64.decode(client_secret))
  
  signature = +t2GOKtZt1hU+C7OGBKZbDOKxds=
  </code></pre>