feat(API): Add optional projectId parameter to credential creation

[everettbu]

Mirror of n8n-io/n8n#21039
Original author: hi120ki

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Summary

Previously, credentials created via the Public API were always saved to the user's personal project.
This change adds an optional projectId parameter to the POST /credentials endpoint, allowing credentials to be created in any project where the user has credential:create permission.

The implementation follows the pattern used in the REST API credential creation endpoint.
If projectId is not provided, the credential is saved to the user's personal project, maintaining backward compatibility.

Related Linear tickets, Github issues, and Community forum posts

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

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Note

Expose optional projectId in credential creation to create credentials in a specified project with permission checks, updating services, OpenAPI, and tests.

• Public API:
  • POST /credentials now accepts optional projectId; handler forwards it to saveCredential and returns proper 403/404 on permission/not-found.
  • OpenAPI updated: request/response schemas include projectId; responses add 403 and 404.
• Services:
  • Credential creation flows switched to ProjectService.getProjectForCredentialCreation to resolve target project and enforce credential:create permissions; removed direct repository checks.
• Tests:
  • Added tests for saveCredential with/without projectId.
  • Added tests for ProjectService.getProjectForCredentialCreation (success, forbidden, not found, optional transaction).

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