Hướng dẫn php base32::encode

I have to pass username as an unique string to a webservice, and the API is asking for the following.

1. Unique string has to be converted to BASE16
2. It is the BASE16 value I have to pass.

I cannot find a way to convert the value to BASE16. PHP does not seem to have a BASE16_ENCODE like it does for BASE64.

Example:

$value = ;
$base16username = base16_encode['$value']; [< Since Base16_encode does not exist, this is my problem]

Google searches are leading me nowhere, nor is the PHP online manual so I suspect I might be overlooking something obvious. Any suggestions?

$ composer require selective/base32