ded response. At least one
   token of data MUST be present.

2.1. Syntax

   In UNIX manual page like syntax, the general form of an extended
   challenge could be described as:

      &lt;standard OTP challenge&gt; ext[,&lt;extension set id&gt;[, ...]]

   And the general form of an extended response could be described as:

      &lt;type-specifier&gt;:&lt;arg1&gt;[:&lt;arg2&gt;[:...]]

   In augmented BNF syntax, the syntax of the general form of an
   extended challenge and an extended response is:

   