user-creation failed if claims does not contain nickname_key (3.8.0 regression)

[drzraf]

Describe the bug
Before 3.8, get_nickname_from_claim would return null if nickname_key (eg: preferred_username) was absent.
create_new_user would, in turn, just set $values_missing or omit setting $nickname.
The user-creation wasn't stopped giving a chance for get_displayname_from_claim.

With 78ede5d#diff-4d7e36ea02368e60c2a32a11344f55b8143ac3656bc95e68204a6fee3bafcdb6R639, then prototype of the function was changed to return WP_Error, but create_new_user wasn't changed accordingly.
(I suggest you look for other errors of this kind in the release)

To Reproduce
Steps to reproduce the behavior:

1. Go to wp/wp-admin/ with an inexistant user
2. Click on Login using openid
3. See error

Screenshots

New user would see the following instead:

Expected behavior
The absence of said claim should fail safely to give a chance to next hook.

Isolating the problem (mark completed items with an [x]):

• I have deactivated other plugins and confirmed this bug occurs when only this plugin is active.
• This bug happens with a default WordPress theme active.
• I can reproduce this bug consistently using the steps above.
• I can confirm that only 3.8.0 is affected. 3.7.0 works as expected (ignore the missing key).

WordPress Environment

• Website URL:
• PHP Version: 7.4
• WordPress Version: 5.4.1
• Plugin Version: 3.8.0
• Identity Provider: Google
• Relevant Plugin Settings:

array (
  'login_type' => 'button',
  'client_id' => '****.apps.googleusercontent.com',
  'client_secret' => '****',
  'scope' => 'email profile openid',
  'endpoint_login' => 'https://accounts.google.com/o/oauth2/v2/auth',
  'endpoint_userinfo' => 'https://www.googleapis.com/oauth2/v3/userinfo',
  'endpoint_token' => 'https://www.googleapis.com/oauth2/v4/token',
  'endpoint_end_session' => 'https://accounts.google.com/o/oauth2/revoke',
  'identity_key' => 'preferred_username',
  'no_sslverify' => '0',
  'http_request_timeout' => '5',
  'enforce_privacy' => '0',
  'alternate_redirect_uri' => '0',
  'nickname_key' => 'preferred_username',
  'email_format' => '{email}',
  'displayname_format' => '',
  'identify_with_username' => '0',
  'link_existing_users' => 1,
  'redirect_user_back' => 1,
  'redirect_on_logout' => '1',
  'enable_logging' => '1',
  'log_limit' => '150',
)

[timnolte]

@drzraf thanks for reporting this, and your analysis. We'll work on a fix.

[drzraf]

May I ask for any news regarding resolving this 3.8.0 regression?