MyRoundcube Calendar Plugin external calendars issues (CalDAV)

Problem:

• MyRoundcube Calendar Plugin is not able to load external calendars which require username and password authentication.
• Adding a new CalDAV calendar gives the following error message:

Failed to save changes.

Failed to establish connection. Please check your data.

• Roundcube setup:
  • Roundcube 1.0.4
  • calendar 19.0.49
  • calendar_plus 4.0.37
  • PHP 5.4.34
  • MySQL 5.5.40

Solution:

• Issue might be the PHP variable open_basedir which is set.
• Either remove open_basedir, or change CURLOPT_FOLLOWLOCATION to false in the corresponding PHP file(s). In this case SabreDAV/lib/Sabre/DAV/Client.php:

326: CURLOPT_FOLLOWLOCATION => false,

Note:

• For more details, see [1], [2] and [3].