Currently, LibreOffice have it's own way to store password and secure them with a master password. But desktop environment on Linux and also Windows and Mac have it's own system.
LibreOffice should use when it's available, the system password manager.
For example a sample program to use it on windows :
I agree with Arnaud. Although there is a bunch of password managers, LibreOffice should at least support the main ones:
- Credential Manager (Windows Vault) on Windows;
- Keychain on OS X;
- kWallet on KDE
- Gnome Keyring for Gnome (do not use Seahorse since it is just a front-end for GPG and SSH).
- Keepass which is a multiplatform and FOSS.
This feature request is obviously for remote file system accesses like WebDAV, CMIS, SMB, etc. not to open a document which is password protected.