title: Client XYZ is configured for secret but secret was not received
body: <p>I'm using AWS PHP SDK and I'm getting this error when trying to signup a new user:</p>
  <p><code>Error executing &quot;SignUp&quot; on &quot;https://cognito-idp.eu-central-1.amazonaws.com&quot;; AWS HTTP error: Client error: `POST https://cognito-idp.eu-central-1.amazonaws.com` resulted in a `400 Bad Request` response: {&quot;__type&quot;:&quot;NotAuthorizedException&quot;,&quot;message&quot;:&quot;Client XYZ is configured for secret but secret was (truncated...)</code></p>
  <p>I've enabled user signup in the settings. Please help.</p>