f-ui: Improve ACL permission error message to prompt sign-in check

[sreekanthkk96]

Description

This PR updates the error message for ACL permission failures to be more actionable by suggesting that users verify they are signed in. Previously, when users encountered a 403 Forbidden error, the message only stated that their ACL token didn't grant permission, which could be confusing for users who weren't logged in at all.

The updated error message now reads: Your ACL token does not grant permission to ${actionMessage}. Please ensure you are signed in.

This change improves the user experience by providing a clear next step when encountering permission errors.

Testing & Reproduction steps

Manual Testing:

1. Open the Nomad UI without being logged in
2. Attempt to perform an action that requires ACL permissions (e.g., accessing jobs, allocations, or other protected resources)
3. Verify that the error message now includes "Please ensure you are signed in."
4. Log in with valid credentials and verify the action works as expected

To reproduce this error message:

1. Use read-only token in the UI
2. Navigate to Jobs and select any job
3. Click "Definition" tab
4. Click "Edit" button
5. Make a change
6. Click "Plan" button
   🐛 YOU SHOULD SEE THE ERROR

Links

• Jira Issue: https://hashicorp.atlassian.net/browse/NMD-1050

Before

After

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad product documentation, which is stored in the
  web-unified-docs repo. Refer to the web-unified-docs contributor guide for docs guidelines.
  Please also consider whether the change requires notes within the upgrade
  guide. If you would like help with the docs, tag the nomad-docs team in this PR.

Reviewer Checklist

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• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

No changes to security controls. This PR only modifies the error message text to be more user-friendly by suggesting users verify they are signed in when encountering ACL permission errors. The underlying authentication and authorization mechanisms remain unchanged.

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[jrasell]

Hi @sreekanthkk96 and thanks for raising this PR.

It solves the direct user issue but I wonder if we can improve upon this by passing an isAuthenticated option to messageFromAdapterError which would allow us to show two distinct messages:

• Not signed in: "You are not signed in. Please sign in to perform this action."
• Signed in, insufficient token → `"Your ACL token does not grant permission to ${actionMessage}."

Curious of your thoughts here on UX and implementation?