# ADR-010: Backward Compatibility for Authentication, Payment, and Authorization

Status: Accepted
Date: 2026-07-03

## Context

Authentication and payment flows are proven and contract-sensitive. Platform refactoring must not break existing integrations.

## Decision

Freeze behavior and contracts for:

- Authentication flow.
- Payment API interactions.
- Authorization logic.

Allow only encapsulation and integration-layer isolation, not contract redesign.

## Consequences

Positive:

- Prevents regressions in critical commerce and access flows.
- Enables architecture modernization around stable core behavior.

Negative:

- Some suboptimal legacy internals may remain until controlled replacement strategy is approved.

## Compliance Requirements

- Existing auth/payment request/response contracts remain unchanged.
- Behavior-equivalent wrappers/adapters are allowed.
- Any change requires explicit ADR and compatibility test evidence.