Purpose Based Access

Root Purpose
├── Service Delivery
│   ├── Order Fulfillment
│   │   ├── Payment Processing
│   │   ├── Shipping Logistics
│   │   └── Order Confirmation
│   ├── Account Management
│   │   ├── Account Creation
│   │   ├── Account Maintenance
│   │   └── Account Recovery
│   └── Customer Support
│       ├── Ticket Resolution
│       └── Escalation Handling
├── Legal Compliance
│   ├── Regulatory Reporting
│   │   ├── Tax Reporting
│   │   ├── AML Compliance
│   │   └── Regulatory Audit
│   ├── Data Subject Rights
│   │   ├── Access Request
│   │   ├── Deletion Request
│   │   ├── Portability Request
│   │   └── Rectification Request
│   └── Litigation Hold
├── Analytics
│   ├── Product Analytics
│   │   ├── Feature Usage Analysis
│   │   └── UX Research
│   ├── Business Intelligence
│   │   ├── Revenue Reporting
│   │   └── Forecasting
│   └── Aggregate Reporting
│       ├── Board Reporting
│       └── Investor Reporting
├── Marketing
│   ├── Direct Marketing
│   │   ├── Email Campaigns
│   │   └── Personalized Offers
│   ├── Market Research
│   │   └── Survey Analysis
│   └── Advertising
│       ├── Audience Segmentation
│       └── Campaign Measurement
└── Security
    ├── Fraud Detection
    ├── Incident Investigation
    └── Access Auditing

from dataclasses import dataclass, field
from enum import Enum
from datetime import datetime


class LegalBasis(Enum):
    CONSENT = "consent"
    CONTRACT = "contract"
    LEGAL_OBLIGATION = "legal_obligation"
    VITAL_INTEREST = "vital_interest"
    PUBLIC_INTEREST = "public_interest"
    LEGITIMATE_INTEREST = "legitimate_interest"


class PurposeStatus(Enum):
    ACTIVE = "active"
    DEPRECATED = "deprecated"
    PENDING_APPROVAL = "pending_approval"


@dataclass
class Purpose:
    purpose_id: str
    name: str
    description: str
    parent_purpose_id: str | None
    legal_bases: list[LegalBasis]
    data_categories_allowed: list[str]
    retention_period_days: int
    requires_consent: bool
    status: PurposeStatus
    owner: str
    created_date: datetime
    review_date: datetime
    jurisdictions: list[str] = field(default_factory=lambda: ["global"])
    compatible_purposes: list[str] = field(default_factory=list)
    incompatible_purposes: list[str] = field(default_factory=list)

Access Request
    |
    v
+-------------------+
| Request Parser    |
| - Identity (who)  |
| - Resource (what) |
| - Action (how)    |
| - Purpose (why)   |
| - Context (when/  |
|   where)          |
+-------------------+
    |
    v
+-------------------+     +--------------------+
| Purpose Validator |---->| Purpose Registry   |
| - Purpose exists  |     | - Ontology tree    |
| - Purpose active  |     | - Legal bases      |
| - Purpose applies |     | - Data categories  |
|   to data category|     +--------------------+
+-------------------+
    |
    v
+-------------------+     +--------------------+
| Consent Checker   |---->| Consent Store      |
| - Consent exists  |     | - Data subject     |
| - Consent active  |     |   preferences      |
| - Scope matches   |     | - Consent records  |
+-------------------+     +--------------------+
    |
    v
+-------------------+     +--------------------+
| ABAC Policy       |---->| Policy Repository  |
| Evaluator         |     | - XACML policies   |
| - Role check      |     | - Purpose-data     |
| - Attribute check  |     |   mappings        |
| - Environment check|     +--------------------+
+-------------------+
    |
    v
+-------------------+
| Decision Engine   |
| - PERMIT / DENY   |
| - Obligations     |
| - Advice          |
+-------------------+
    |
    +------+-------+
    |              |
    v              v
PERMIT          DENY
+ Audit Log     + Audit Log
+ Obligations   + Denial Reason

"""
Purpose-Based Access Control policy engine.
Evaluates access requests against purpose definitions,
consent records, and attribute-based policies.
"""

from dataclasses import dataclass
from datetime import datetime
from enum import Enum
from typing import Optional


class Decision(Enum):
    PERMIT = "PERMIT"
    DENY = "DENY"


@dataclass
class AccessRequest:
    requester_id: str
    requester_roles: list[str]
    resource_id: str
    data_category: str
    action: str  # read, write, delete, export
    purpose_id: str
    data_subject_id: Optional[str]
    timestamp: datetime
    source_ip: str
    justification: str


@dataclass
class AccessDecision:
    decision: Decision
    reason: str
    obligations: list[str]
    request: AccessRequest
    evaluated_at: datetime
    policy_version: str


class PurposeBasedAccessController:
    """
    Core PBAC engine that evaluates access requests against
    purpose definitions, consent records, and organizational policies.
    """

    def __init__(
        self,
        purpose_registry,
        consent_store,
        policy_repository,
        audit_logger
    ):
        self.purpose_registry = purpose_registry
        self.consent_store = consent_store
        self.policy_repository = policy_repository
        self.audit_logger = audit_logger

    def evaluate(self, request: AccessRequest) -> AccessDecision:
        """
        Evaluate an access request through the PBAC pipeline.

        Pipeline stages:
        1. Purpose validation
        2. Consent verification
        3. Attribute-based policy evaluation
        4. Decision with obligations
        """
        now = datetime.utcnow()

        # Stage 1: Validate purpose
        purpose = self.purpose_registry.get_purpose(request.purpose_id)
        if purpose is None:
            return self._deny(request, "Purpose not found in registry", now)

        if purpose.status != PurposeStatus.ACTIVE:
            return self._deny(request, f"Purpose is {purpose.status.value}", now)

        if request.data_category not in purpose.data_categories_allowed:
            return self._deny(
                request,
                f"Data category '{request.data_category}' not allowed for purpose '{purpose.name}'",
                now
            )

        # Stage 2: Verify consent (if required)
        if purpose.requires_consent and request.data_subject_id:
            consent = self.consent_store.get_active_consent(
                data_subject_id=request.data_subject_id,
                purpose_id=request.purpose_id
            )
            if consent is None:
                return self._deny(
                    request,
                    f"No active consent for purpose '{purpose.name}' from data subject",
                    now
                )

        # Stage 3: Evaluate attribute-based policies
        policy_result = self.policy_repository.evaluate(
            roles=request.requester_roles,
            resource=request.resource_id,
            action=request.action,
            purpose=request.purpose_id,
            data_category=request.data_category,
            context={"source_ip": request.source_ip, "time": now}
        )

        if not policy_result.permitted:
            return self._deny(request, policy_result.denial_reason, now)

        # Stage 4: Permit with obligations
        obligations = self._determine_obligations(purpose, request)
        decision = AccessDecision(
            decision=Decision.PERMIT,
            reason=f"Access permitted for purpose '{purpose.name}'",
            obligations=obligations,
            request=request,
            evaluated_at=now,
            policy_version=self.policy_repository.version
        )

        self.audit_logger.log_access_decision(decision)
        return decision

    def _deny(
        self, request: AccessRequest, reason: str, timestamp: datetime
    ) -> AccessDecision:
        """Create a DENY decision and log it."""
        decision = AccessDecision(
            decision=Decision.DENY,
            reason=reason,
            obligations=[],
            request=request,
            evaluated_at=timestamp,
            policy_version=self.policy_repository.version
        )
        self.audit_logger.log_access_decision(decision)
        return decision

    def _determine_obligations(self, purpose, request: AccessRequest) -> list[str]:
        """Determine post-access obligations based on purpose and context."""
        obligations = []

        if request.action == "export":
            obligations.append("LOG_DATA_EXPORT")
            obligations.append("APPLY_ENCRYPTION_TO_EXPORT")

        if request.action == "read" and request.data_category in [
            "health_data", "financial_data", "biometric_data"
        ]:
            obligations.append("MASK_SENSITIVE_FIELDS")

        obligations.append(f"ENFORCE_RETENTION_{purpose.retention_period_days}_DAYS")
        obligations.append("LOG_PURPOSE_USAGE")

        return obligations

"""
SQL proxy that intercepts database queries and enforces
purpose-based access control at the query level.
"""

import re
from datetime import datetime


class PurposeAwareSQLProxy:
    """
    Intercepts SQL queries, validates purpose, and rewrites
    queries to enforce data category restrictions.
    """

    def __init__(self, pbac_controller, column_category_map: dict):
        self.pbac = pbac_controller
        self.column_category_map = column_category_map

    def execute_query(
        self,
        sql: str,
        requester_id: str,
        requester_roles: list[str],
        purpose_id: str,
        justification: str
    ) -> tuple[bool, object]:
        """
        Execute a SQL query with purpose verification.

        Returns (success, result_or_error).
        """
        # Parse referenced columns/tables from SQL
        referenced_columns = self._extract_columns(sql)
        referenced_categories = set()

        for col in referenced_columns:
            category = self.column_category_map.get(col, "general")
            referenced_categories.add(category)

        # Validate access for each data category
        denied_categories = []
        for category in referenced_categories:
            request = AccessRequest(
                requester_id=requester_id,
                requester_roles=requester_roles,
                resource_id="database",
                data_category=category,
                action="read",
                purpose_id=purpose_id,
                data_subject_id=None,
                timestamp=datetime.utcnow(),
                source_ip="internal",
                justification=justification
            )

            decision = self.pbac.evaluate(request)
            if decision.decision == Decision.DENY:
                denied_categories.append((category, decision.reason))

        if denied_categories:
            reasons = "; ".join(
                f"{cat}: {reason}" for cat, reason in denied_categories
            )
            return (False, f"Access denied for categories: {reasons}")

        # Rewrite query to mask unauthorized columns if needed
        rewritten_sql = self._apply_column_masking(sql, purpose_id)

        # Execute the rewritten query (actual DB execution would go here)
        return (True, rewritten_sql)

    def _extract_columns(self, sql: str) -> list[str]:
        """Extract column references from SQL (simplified parser)."""
        select_pattern = re.compile(
            r"SELECT\s+(.+?)\s+FROM", re.IGNORECASE | re.DOTALL
        )
        match = select_pattern.search(sql)
        if not match:
            return []

        columns_str = match.group(1)
        if columns_str.strip() == "*":
            return list(self.column_category_map.keys())

        columns = [
            col.strip().split(".")[-1].split(" ")[0]
            for col in columns_str.split(",")
        ]
        return columns

    def _apply_column_masking(self, sql: str, purpose_id: str) -> str:
        """Rewrite query to mask columns not needed for the given purpose."""
        return sql  # Production implementation would rewrite SELECT columns

Existing IAM (RBAC/ABAC)
    |
    v
+---------------------------+
| PBAC Middleware Layer      |
| (intercepts access calls) |
+---------------------------+
    |
    +-- Purpose verification
    +-- Consent validation
    +-- Data category mapping
    +-- Obligation enforcement
    +-- Enhanced audit logging
    |
    v
Resource (Database / API / File System)