"Validation failed: Last name can't be blank" when trying to use OIDC

Describe the bug

I'm getting a "Validation failed: Last name can't be blank" exception when trying to use OIDC.

To Reproduce

Configure your OIDC server so that it returns a name without any whitespace
Try to log in using OIDC
Observe crash

Expected behaviour

usernames without whitespace are supported.

Environment details

OS: all
Browser: all
Version: 3.3.4

Temporary workaround for people facing this issue

change the oidc.name_field option to some random value that doesn't exist, doing so will prevent the names from being updated

Additional information/context

the OIDC spec specifies the name field as End-User's full name in displayable form including all name parts, possibly including titles and suffixes, ordered according to the End-User's locale and preferences. so we can't assume that it will be in any particular format. And even if we do, the name field is configurable via the uidc.name_field option and a user might want to use something like preferred_username instead, and that rarely will have any whitespace. The spec also includes given_name, family_name, and middle_name as part of the Standard Claims but not every provider supports them. See: https://openid.net/specs/openid-connect-core-1_0.html#rfc.section.5.1

I have 10+ services configured in my OIDC provider and all of them can handle usernames just fine. Imo assuming anything about the name field is a recipe for disaster. The spec even mentions possibly including titles and suffixes, ordered according to the End-User's locale and preferences., and people all over the world can have different formats, prefixes, suffixes, middle names, etc.

problematic line: https://github.com/postalserver/postal/blob/da90e75036c27482699921613d838f4058a100e7/app/models/user.rb#L127

trace:

[...]
/usr/local/bundle/gems/activerecord-7.0.8.1/lib/active_record/suppressor.rb:54:in `save!'
/opt/postal/app/app/models/user.rb:129:in `find_from_oidc'
/opt/postal/app/app/controllers/sessions_controller.rb:76:in `create_from_oidc'
/usr/local/bundle/gems/actionpack-7.0.8.1/lib/action_controller/metal/basic_implicit_render.rb:6:in `send_action'
[...]

log (details redacted with <REDACTED>):

D, [2024-07-21T17:34:00.071792 #10] DEBUG -- omniauth: (oidc) Callback phase initiated.
2024-07-21 17:34:00 +0000 DEBUG  got auth details from issuer: #<OmniAuth::AuthHash amr=#<Hashie::Array ["pwd", "pop", "hwk", "user", "pin", "mfa"]> at_hash="<REDACTED>" aud=#<Hashie::Array ["postal"]> auth_time=1719762174 azp="postal" client_id="postal" email="nezu@<REDACTED>" email_verified=true exp=1721586840 groups=#<Hashie::Array ["admin", "<REDACTED>"]> iat=1721583240 iss="https://auth.<REDACTED>" jti="<REDACTED>" name="nezu" nonce="<REDACTED>" preferred_username="nezu" sub="<REDACTED>">
2024-07-21 17:34:00 +0000 DEBUG  no user with UID <REDACTED> for issuer https://auth.<REDACTED>
2024-07-21 17:34:00 +0000 DEBUG  found user with e-mail address nezu@<REDACTED> (user ID: 1)
2024-07-21 17:34:00 +0000 ERROR  GET /auth/oidc/callback?code=<REDACTED>&iss=https%3A%2F%2Fauth.<REDACTED>&scope=openid+profile+email+groups&state=<REDACTED> (422) event=request transaction=<REDACTED> controller=SessionsController action=create_from_oidc format=html method=GET path=/auth/oidc/callback?code=<REDACTED>&iss=https%3A%2F%2Fauth.<REDACTED>&scope=openid+profile+email+groups&state=<REDACTED> request_id=<REDACTED> ip_address=<REDACTED> status=422 db_runtime=4.355344772338867 exception_class=ActiveRecord::RecordInvalid exception_message=Validation failed: Last name can't be blank exception_backtrace=/usr/local/bundle/gems/activerecord-7.0.8.1/lib/active_record/validations.rb:80:in `raise_validation_error'\n/usr/local/bundle/gems/activerecord-7.0.8.1/lib/active_record/validations.rb:53:in `save!'\n/usr/local/bundle/gems/activerecord-7.0.8.1/lib/active_record/transactions.rb:302:in `block in save!'\n/usr/local/bundle/gems/activerecord-7.0.8.1/lib/active_record/transactions.rb:354:in `block in with_transaction_returning_status'
2024-07-21 17:34:00 +0000 Rack app ("GET /auth/oidc/callbackcode=<REDACTED>&iss=https%3A%2F%2Fauth.<REDACTED>&scope=openid+profile+email+groups&state=<REDACTED>" - (<REDACTED>)): #<ActiveRecord::RecordInvalid: Validation failed: Last name can't be blank>

postalserver / postal