Authentication, rate limits and provider spend controls

[TechBeme]

Goal

Provide reusable protection for public Open-Higgsfield deployments that use paid provider credentials.

Scope

• Add an authentication adapter boundary.
• Add per-user and per-IP generation rate limits.
• Add configurable provider/model allowlists.
• Add daily or monthly spend/usage limits where provider metadata permits it.
• Return clear, provider-neutral limit errors to the UI.

Acceptance criteria

• Security controls are opt-in for local development and documented for production.
• API keys remain server-only.
• Limits work consistently across image and video routes.
• Tests cover bypass and concurrency scenarios.