<?php
function jabbajabbab() {

  $url = 'http://some-site.com:1359/api/groups/jabbajabba';
  $content = file_get_contents($url);
  $json = json_decode($content, true);

  foreach($json['some_data'] as $item) {
    print $item['registration_date'];
    print 'some text';
  }
}
add_action( 'bp_before_group_header_meta', 'jabbajabbab' );
?>