Standalone System - use authx_login for authenticate flow

[ufundo]

Overview

Use the authx_login flow in CRM_Utils_System_Standalone::authenticate - so we have a common codepath for all logins.

Before

• a bespoke implementation of the login flow here

After

• use the canonical one from authx extension

Technical Details

@totten noted this will mean the login is subject to AuthX policies. The pertinent one is if password isn't enabled as a credential type, then it will not be accepted. However you also wouldn't be able to log in to your Standalone site through the web UI - so seems an unlikely edge case.

I'm not totally sure what flows through this function. @totten mentioned cron.php - though that is deprecated and won't work on Standalone for other reasons.

[civibot]

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[ufundo]

Thanks @colemanw

Upgrade tests are failing on master