Consent flow skipped during SSO user registration if username is left at default

[AndrewFerr]

Description

When using an SSO mapping provider that automatically sets a new user's mxid localpart (as opposed to prompting the user to choose it), then requiring consent tracking on new user registration doesn't work: registering a new user via SSO does not prompt for consent & lets the registration finish as if consent was not required.

Steps to reproduce

• Follow the steps to enable the user consent flow and to make it mandatory on new user registration.
• Configure a SSO mapping provider that returns a mxid localpart
• Register a new user via SSO

Expected results: The registration flow should eventually open a webpage at /_matrix/consent and not register a new user until the consent form on that page has been submitted.

Actual results: The registration will complete without prompting for consent, as if user_consent.require_at_registration was not set. Other consent configurations still take affect, though, such as user_consent.block_events_error.

Version information

• Homeserver: Self-hosted

If not matrix.org:

• Version: 1.41.1

• Install method: git clone

• Platform: Fedora 34