Update xmlseclibs requirement to ^4.0 due GHSA-m5mw-mr39-66vp

[scybulski]

Description

Summary

#654

Upgrades robrichards/xmlseclibs from ^3.1.5 to ^4.0 to address a critical signature-forgery vulnerability. Adds a new security.allowRSA15KeyTransport setting (default false) so deployments with legacy IdPs that still use RSA-1.5 key transport can opt in during migration, while secure defaults remain unchanged.

Security

This addresses:

• AIKIDO-2026-134354
• GHSA-m5mw-mr39-66vp — RSA-to-HMAC algorithm substitution in xmlseclibs < 4.0.0; fixed in 4.0.0

xmlseclibs 4 also denies RSA-1.5 key transport by default (Bleichenbacher risk). This PR maps that behavior to an explicit toolkit setting rather than silently breaking encrypted assertions/NameIDs for legacy peers.

Changes

• Bump robrichards/xmlseclibs to ^4.0
• Bump minimum PHP to >=8.0 (required by xmlseclibs 4)
• Add security.allowRSA15KeyTransport (default false); documented in advanced_settings_example.php
• Wire the setting through decryption paths:
  • Utils::decryptElement() / Utils::createDecryptionContext()
  • Response (encrypted assertions and encrypted NameIDs)
  • LogoutRequest::getNameIdData(), getNameId(), and isValid()
• Update CHANGELOG under [UNRELEASED]
• Update tests for xmlseclibs 4 error-message changes; add OAEP and RSA-1.5 fixtures covering default, opt-in, and blocked behavior

Breaking changes

• PHP >=8.0 required (was >=7.3)
• RSA-1.5 encrypted assertions/NameIDs fail by default unless security.allowRSA15KeyTransport => true is set for a given IdP/integration

Migration notes

For most deployments, no config change is needed.

If decryption fails with "RSA-1.5 key transport is disabled":

1. Prefer reconfiguring the IdP to use RSA-OAEP where possible.
2. Only if that is not feasible, enable per-integration:

'security' => [
    'allowRSA15KeyTransport' => true,
],

This mirrors xmlseclibs 4 guidance: use algorithm allowlists / secure defaults, and enable legacy RSA-1.5 only temporarily while migrating peers.

Test plan

• ./vendor/bin/phpunit — 300 tests, 1330 assertions
• OAEP encrypted NameID fixtures decrypt with default settings
• RSA-1.5 fixtures decrypt only with allowRSA15KeyTransport => true
• RSA-1.5 fixtures rejected when the setting is false

References

• xmlseclibs 4.0 advisory: GHSA-m5mw-mr39-66vp
• Prior advisory-driven bumps in this repo: v4.3.2 (xmlseclibs 3.1.5), v4.3.1 (xmlseclibs 3.1.4)

[pitbulk]

Thanks @scybulski for the collaboration, I will review carefully and merge asap.