config: keep local SMTP auth secret overrides

[sueun-dev]

A receiver-level auth_secret should override the global SMTP auth secret defaults. The loader currently merges auth_secret and auth_secret_file independently, though, so a receiver with a local inline secret also inherits global.smtp_auth_secret_file.

That leaves both fields set. getAuthSecret checks the file first, so the receiver's inline secret is not used. If the global path is unavailable, the notification fails while trying to read it; if it is available, CRAM-MD5 uses the global file contents instead of the receiver override.

This restores paired inheritance: copy the global secret fields only when neither receiver field is set, matching the existing password/password-file handling. The global/local SMTP fixture now covers a global secret file with both local inline-secret and local secret-file overrides.

Tested with:

• go test ./config/ -run '^TestGlobalAndLocalSMTPPassword$' -count=1
• go test ./config/... ./notify/email/... -count=1
• go test -race ./config/... ./notify/email/... -count=1
• go vet ./config/... ./notify/email/...
• go build ./config/... ./notify/email/... ./cmd/amtool

Pull Request Checklist

• Please list all open issue(s) discussed with maintainers related to this change
  • None
• Is this a new Receiver integration?
  • I have already tried to use the Webhook Receiver Integration and third-party integrations before adding this new Receiver Integration
• Is this a bugfix?
  • I have added tests that can reproduce the bug which pass with this bugfix applied
• Is this a new feature?
  • I have added tests that test the new feature's functionality
• Does this change affect performance?
  • I have provided benchmarks comparison that shows performance is improved or is not degraded
  • I have added new benchmarks if required or requested by maintainers
• Is this a breaking change?
  • My changes do not break the existing cluster messages
  • My changes do not break the existing api
• I have added/updated the required documentation
  • Not needed: the current docs already say auth_secret and auth_secret_file are mutually exclusive.
• I have signed-off my commits
• I will follow best practices for contributing to this project

Which user-facing changes does this PR introduce?

[BUGFIX] Email: Honor a receiver's inline `auth_secret` when a global `smtp_auth_secret_file` is configured.

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 55d0d79 and 1968855.

📒 Files selected for processing (3)

• config/config.go
• config/config_test.go
• config/testdata/conf.smtp-password-global-and-local.yml

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📝 Walkthrough

Walkthrough

SMTP receiver authentication secrets now inherit global values only when both receiver-level fields are unset. Tests and test data cover inheritance and mutual clearing between inline secrets and secret files.

Changes

SMTP secret inheritance

Layer / File(s)	Summary
Paired SMTP secret resolution config/config.go, config/config_test.go, config/testdata/conf.smtp-password-global-and-local.yml	SMTP AuthSecret and AuthSecretFile inherit global values together. Local inline or file settings clear the corresponding inherited value. Tests and fixture data cover these cases.

Estimated code review effort: 2 (Simple) | ~10 minutes

Mergeability Score: ⚪ Minimal · up to 19688

This change makes receiver-level SMTP authentication secrets take precedence over global defaults, with no actionable merge-blocking risk remaining after normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description explains the bug, implementation, tests, checklist status, documentation rationale, and release notes.
Title check	✅ Passed	The title clearly identifies the configuration area and the primary change to preserve local SMTP authentication secret overrides.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[SoloJacobs]

@TheMeier Hmm, looks like we broke this one: #4812
Perhaps there are more similar regressions?

[TheMeier]

@TheMeier Hmm, looks like we broke this one: #4812 Perhaps there are more similar regressions?

Yes very likely. :( I really think we should make a formal abstraction for merging configs. Something like this 7454fd5