Customer Login Page is incorrectly cached with private data if Magento Captcha isn't enabled

[collymore]

Preconditions and environment

• Version 2.4.7

Steps to reproduce

• Disable the module Magento_Captcha, there is no dependancy on this module and the Magento_Customer module, so the Customer Login page should work correctly.
• Visit the Customer Account login page "/customer/account/login" with Full page cache active

Expected result

The page returns FPC MISS.

The customer account form is using private data e.g The current Customer Email address is output in the forms login field" and this shouldn't be cached.

Actual result

The page response is returned with a Full page cache HIT.

If visiting the page after a cache clear and logged in, the email will be cached on the page for all subsequent requests.

Additional information

The only reason that the Customer Account Login page is not cached by default is the Magento_Captcha module's layout customer_account_login.xml file.

This is adding a bock name="captcha" to the container name="form.additional.info".
That block has cacheable="false" declared which then stops the login page from being cached.

Without this module activate nothing else is making the page non-cacheable.

Edit : This issue actually effects every Customer Account Form

Release note

No response

Triage and priority

• [ ] Severity: S0 - Affects critical data or functionality and leaves users without workaround.
• [X] Severity: S1 - Affects critical data or functionality and forces users to employ a workaround.
• [ ] Severity: S2 - Affects non-critical data or functionality and forces users to employ a workaround.
• [ ] Severity: S3 - Affects non-critical data or functionality and does not force users to employ a workaround.
• [ ] Severity: S4 - Affects aesthetics, professional look and feel, “quality” or “usability”.

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