У каждого радиоведущего свой пароль для вещания.

    <mount>
        <mount-name>/demostream</mount-name>
        <max-listeners>100</max-listeners>
        <fallback-mount>/nonstop</fallback-mount>
        <fallback-override>1</fallback-override>
     <charset>UTF8</charset>
      <hidden>0</hidden>
         <authentication type="url">
              <option name="stream_auth" value="http://localhost/source_auth.php"/>
              <option name="auth_header" value="icecast-auth-user: OK"/>
              <option name="user" value="source"/>
         </authentication>
    </mount>

$port=$_POST['port'];
$password_req=$_POST['pass'];
$allowed_passwords=array();
$allowed_passwords[]='pass1';
$allowed_passwords[]='pass2';
$allowed_passwords[]='pass3';
if(in_array($password_req,$allowed_passwords))
{
    header('icecast-auth-user: OK');
    header('icecast-auth-message: Auth is succesful');
}
else
{
    header('icecast-auth-message: Auth is failed');
}