coulomb-social/coulomb_social/apps/identity/flex_auth.py

"""flex-auth PEP — check actions via POST /v1/check (fail-closed).

Vocabulary (minimal for shell / CSOC-WP-0002-T07):

| action            | resource.type | When allowed (local mode)      |
|-------------------|---------------|--------------------------------|
| shell:view        | shell         | any authenticated principal    |
| member:self:read  | member        | subject matches resource id    |
| member:admin      | member        | deny until policy package live |

When FLEX_AUTH_BASE_URL is set, all checks go to the PDP. Transport or
malformed responses → deny.
"""

from __future__ import annotations

import json
import uuid
from dataclasses import dataclass
from typing import Any
from urllib.error import HTTPError, URLError
from urllib.request import Request, urlopen

from django.conf import settings


@dataclass(frozen=True)
class AuthzDecision:
    allow: bool
    reason: str
    decision_id: str = ""
    effect: str = ""


def check(
    action: str,
    *,
    resource: str = "shell",
    resource_id: str = "default",
    subject: str = "",
    tenant: str = "",
    subject_type: str = "human",
    attributes: dict[str, Any] | None = None,
) -> AuthzDecision:
    """Decide whether `action` is allowed for the subject on the resource."""
    tenant = tenant or settings.DEFAULT_TENANT_ID
    system_id = settings.FLEX_AUTH_PROTECTED_SYSTEM_ID
    base = (settings.FLEX_AUTH_BASE_URL or "").strip()

    if not base:
        return _local_check(
            action,
            resource=resource,
            resource_id=resource_id,
            subject=subject,
        )

    return _http_check(
        action,
        resource=resource,
        resource_id=resource_id,
        subject=subject,
        tenant=tenant,
        subject_type=subject_type,
        system_id=system_id,
        attributes=attributes or {},
    )


def _local_check(
    action: str,
    *,
    resource: str,
    resource_id: str,
    subject: str,
) -> AuthzDecision:
    if action == "shell:view" and resource == "shell":
        return AuthzDecision(
            allow=True,
            reason="local-shell-view-authenticated",
            effect="allow",
            decision_id=f"local_{uuid.uuid4().hex[:12]}",
        )
    if action == "member:self:read" and resource == "member":
        if subject and resource_id and subject == resource_id:
            return AuthzDecision(
                allow=True,
                reason="local-member-self-read",
                effect="allow",
                decision_id=f"local_{uuid.uuid4().hex[:12]}",
            )
        return AuthzDecision(
            allow=False,
            reason="local-member-self-mismatch",
            effect="deny",
        )
    return AuthzDecision(
        allow=False,
        reason="local-fail-closed-unknown-action",
        effect="deny",
    )


def _http_check(
    action: str,
    *,
    resource: str,
    resource_id: str,
    subject: str,
    tenant: str,
    subject_type: str,
    system_id: str,
    attributes: dict[str, Any],
) -> AuthzDecision:
    decision_id = f"req_{uuid.uuid4().hex}"
    payload = {
        "id": decision_id,
        "tenant": tenant,
        "subject": {
            "id": subject or "anonymous",
            "type": subject_type,
            "tenant": tenant,
            "attributes": attributes,
        },
        "action": action,
        "resource": {
            "id": resource_id,
            "type": resource,
            "system": system_id,
            "tenant": tenant,
            "attributes": {},
        },
        "context": {"application_id": settings.USER_ENGINE_APPLICATION_ID},
    }
    url = f"{settings.FLEX_AUTH_BASE_URL.rstrip('/')}/v1/check"
    timeout = float(getattr(settings, "FLEX_AUTH_TIMEOUT_SECONDS", 3.0))
    try:
        with urlopen(
            Request(
                url,
                data=json.dumps(payload).encode(),
                headers={"Content-Type": "application/json", "Accept": "application/json"},
                method="POST",
            ),
            timeout=timeout,
        ) as resp:
            body = json.load(resp)
        effect = str(body.get("effect") or "deny").lower()
        allow = effect == "allow"
        return AuthzDecision(
            allow=allow,
            reason=str(body.get("reason") or "flex-auth"),
            decision_id=str(body.get("id") or decision_id),
            effect=effect,
        )
    except (HTTPError, URLError, TimeoutError, ValueError, KeyError, TypeError, json.JSONDecodeError):
        return AuthzDecision(
            allow=False,
            reason="flex-auth-unavailable-fail-closed",
            decision_id=decision_id,
            effect="deny",
        )