[19.0] Normalize falsey smtp_authentication to disable SMTP auth
What does this MR do and why?
This backports !9516 (merged) and !9521 (merged) to 19-0-stable.
When gitlab_rails['smtp_authentication'] was set to false, the
smtp_settings.rb template rendered it via to_s.to_sym, producing the
symbol :false. With net-smtp 0.5.x, Net::SMTP#start validates any
truthy authtype against its known SASL mechanisms and raises
ArgumentError: wrong authentication type false. Earlier net-smtp
versions (e.g. 0.3.3) silently ignored the value, so this only surfaced
after the upgrade.
Normalize the setting at config-parse time in SmtpHelper instead of
branching in the template: falsey/"disable" values (false, 'false',
'none', '') become nil so no authentication: line is rendered,
while real mechanisms are passed through unchanged. This keeps the
template declarative and moves the decision logic into tested Ruby.
Describe in detail what merge request is being backported and why
MR acceptance checklist
This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.
- This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
- The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
- This MR has a severity label assigned (if applicable).
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