feat(reader-auth): send WP login reminder email to non-reader accounts

[dkoo]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Addresses some persistent confusion expressed by publishers who are trying to use reader-based login and registration flows to log into their non-reader (admin, editor, author, etc.) accounts. In this scenario, we can send the user an email to remind them to log in via the regular WP login page instead of reader-facing UIs.

How to test the changes in this Pull Request:

1. Check out this branch.
2. Visit Newspack > Engagement > Reader Activation > Advanced Settings > Transactional Email Content and confirm there's a new "Non-reader account" email at the bottom of the list.

3. Edit this email and confirm it looks something like this:

4. In a new incognito session, attempt to register a reader account via the Registration block using an email address already associated with an admin, editor, or author user account. Confirm that you see the message that the account is already registered:

5. Check the email inbox associated with the email address and confirm that you got the reminder email as in step 3. Confirm that the "Continue to [Site Name]" button leads to the WP login form page.
6. In the incognito session, attempt to login and register via the "Sign In" modal. Confirm that you see the following when attempting to login or register, and that in either case you get the reminder email in the email address's inbox:

Logging in (note: we could show a message directing the user to check their email here instead, if desired):

Registering:

7. Update and save the email template in step 3, repeat steps 4-5, and confirm that the sent reminder email matches the updated content.
8. Try to register via the Sign In modal with an existing reader account email address and confirm that you see the following messages depending on whether the reader account has set a password:

Has a password:

No password:

9. Smoke test registering a new reader account and logging into an existing reader account using both password and OTP.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[adekbadek]

publishers who are trying to use reader-based login and registration flows to log into their non-reader (admin, editor, author, etc.) accounts

I assume the reason for the email solution is because we don't want to enable fishing for admin email addresses. Just noting because I'd expect that noted somewhere, preferably in the code.

I think the reminder email content should be more explicit about using the /wp-admin link and point out that the user tried to use a login flow reserved for readers.

[adekbadek]

I see instances of https://dkoo.jurassic.tube?np_newsletters_click in the body here. Should be removed.

[dkoo]

Whoops, thanks for catching! Fixed in 8a827ac.

[adekbadek]

This comment should be updated to explain the new condition.

[dkoo]

Added an explanation in 458121d. Also made the email message more explicit in 8f96cc4:

Someone attempted to sign into your account on SITE_TITLE using a login method reserved for reader accounts. Please use the following link to sign in via the WordPress admin dashboard:

[dkoo]

Thanks for the feedback, @adekbadek! I've responded in the threads above.