Expose registration mode through Back Office operational configuration

[yacosta738]

Context

The first approved dynamic configuration in the RFC is registration.mode. Back Office should expose selected runtime configuration safely, without becoming a generic environment-variable editor.

Goal

Implement operational configuration support for registration mode and expose the admin command/query path required to manage it safely.

Scope

• Expose registration.mode for administrative read and write.
• Support OPEN, INVITE_ONLY, and CLOSED values.
• Record configuration changes with audit detail including previous and new values.
• Enforce authorization for configuration changes.

Out of Scope

• Arbitrary environment-variable editing.
• Secret management.
• Unapproved runtime configuration unrelated to current operational needs.

Domain Rules

• Registration policy remains mutually exclusive state.
• Configuration changes must be explicit and auditable.
• Only approved dynamic configuration belongs in Back Office.

API Contract

• Prefer explicit admin query/update contract for registration mode.
• Configuration writes must validate allowed values.

Security

• Requires explicit configuration write permission.
• Server-side validation required.

Audit

• Emit CONFIGURATION_CHANGED events containing the key and before/after values.

Observability

• Configuration changes should be logged with correlation IDs.

Acceptance Criteria

1. Administrators can read the current registration mode.
2. Authorized administrators can change registration mode between OPEN, INVITE_ONLY, and CLOSED.
3. Unauthorized attempts are rejected.
4. Configuration changes are audited with previous and new values.

Gherkin

Feature: Operational registration mode configuration

  Scenario: Change registration mode
    Given registration mode is "OPEN"
    When an authorized administrator changes it to "INVITE_ONLY"
    Then new registrations should require an invitation
    And the change should be audited

Testing

• Application
• API
• Integration
• Security

Dependencies

• Introduce registration policy abstraction for OPEN, INVITE_ONLY, and CLOSED #658
• Implement administrative audit event infrastructure #657

References

• RFC sections 15, 27, 28, 30, 31, 45

[linear-code]

DALLAY-576