source3/libsmb: split domain\user in smbc_set_credentials_with_fallback

Clemens Brunnerrequested to merge
cbrnr/samba:split into master

When passing a domain-qualified username like DOMAIN\user or DOMAIN/user to smbc_set_credentials_with_fallback(), the domain prefix was previously stored as part of the username. This caused authentication failures on DFS shares where the target server is different from the entry-point server, because those connections use the context-level credentials directly and would try to authenticate as the literal string DOMAIN\user with no domain set. I've stumbled upon this behavior using Dolphin (with the Samba part in KIO-Extras) and initially tried to fix it there (https://invent.kde.org/network/kio-extras/-/merge_requests/517), but I think the fix belongs here.

This patch splits the username on \, /, or the configured winbind separator, storing the domain and username in their respective credential fields (this mirrors what cli_session_creds_init() already does for initial connections). If the caller explicitly supplied a non-default workgroup, that value takes precedence over any domain embedded in the username.

Checklist

  • Commits have Signed-off-by: with name/author being identical to the commit author
  • (optional) This MR is just one part towards a larger feature.
  • (optional, if backport required) Bugzilla bug filed and BUG: tag added
  • Test suite updated with functionality tests
  • Test suite updated with negative tests
  • Documentation updated
  • CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

  • There is a test suite reasonably covering new functionality or modifications
  • Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
  • This feature/change has adequate documentation added
  • No obvious mistakes in the code

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