(federation file sharing) cannot share file to user with @ in username

[p5n]

Steps to reproduce

1. Set up 2 nextcloud instances
2. Use IMAP external authentication with IMAP server that uses user@domain usernames
3. Try to share file to user@domain@cloud.domain

Expected behaviour

File shared

Actual behaviour

Nothing happened: file looks shared, but another instance does not get it. However it works for other nextcloud instances that does not use IMAP external auth.

Server configuration

Operating system:
ArchLinux

Web server:
nginx and apache

Database:
mariadb

PHP version:
7.2.1

Nextcloud version: (see Nextcloud admin page)
13.0.4

[nextcloud-bot]

GitMate.io thinks possibly related issues are #6707 (User cannot move shared file to shared folder), #9789 ([Request]Add options to hide or change user name in shared files 'file shared by user'), #9628 (Shared file saved at wrong user.), #1708 (Sharing: Cannot delete files from share ), and #9698 (Search is not working in Shared Folders by Other users).

[MorrisJobke]

cc @schiessle @nextcloud/sharing

[p5n]

This strange but after some time I received notification and was able to accept file. I am closing it now and continue testing