tomevault-io Session-Based Access Control Security Pattern
Combines session-based authentication (opaque tokens) with authorization. Subject is first authenticated via session ID, then authorized based on their principal's privileges before action execution.
Core Components
| Role | Type | Responsibility |
|---|---|---|
| Subject | Entity | Requests actions with session ID |
| Authentication Enforcer | Enforcement Point | Verifies session ID |
| Verifier | Decision Point | Validates session, retrieves principal |
| Session Manager | Entity | Maintains open sessions |
| Session ID Generator | Cryptographic Primitive | Generates secure session IDs |
| Authorisation Enforcer | Enforcement Point | Checks action authorization |
| Decider | Decision Point | Makes authorization decisions |
| Policy Provider | Information Point | Manages access policies |
Data Elements
- sessionId: Opaque token identifying session
- principal: Authenticated identity
- actionId: Identifier for requested action
- objectId: Identifier for target resource
- privileges: Permissions granted to principal
Combined Flow
Subject → [action + sessionId] → Auth Enforcer
Auth Enforcer → [sessionId] → Verifier
Verifier → [get_principal] → Session Manager
Session Manager → [principal] → Verifier
Verifier → [principal] → Auth Enforcer
Auth Enforcer → [action + principal] → Authz Enforcer
Authz Enforcer → [authorise(principal, actionId, objectId)] → Decider
Decider → [get_privileges(principal)] → Policy Provider
Policy Provider → [privileges] → Decider
Decider → [allowed/denied] → Authz Enforcer
Authz Enforcer → [action] → System (if allowed)
Step-by-Step
- Subject sends request with session ID
- Authentication Enforcer forwards session ID to Verifier
- Verifier queries Session Manager for associated principal
- If valid session, principal returned to Auth Enforcer
- Auth Enforcer forwards request (with principal) to Authz Enforcer
- Authz Enforcer extracts actionId and objectId from request
- Decider queries Policy Provider for principal's privileges
- Decider determines if action on object is permitted
- If authorized, request forwarded to System
Session Management
Session Creation
- Subject authenticates (e.g., password login)
- Session Manager creates new session
- Session ID Generator produces secure random ID
- Session Manager stores sessionId→principal mapping
- Session ID returned to Subject
Session ID Requirements
- Minimum 64 bits of entropy
- Generate 128+ bits using CSPRNG
- Check for duplicates before storing
Session Lifetime
- Idle timeout (configurable)
- Absolute maximum duration
- Invalidate on logout
- Invalidate on credential change
Authorization Model
Privilege Determination
- Policy Provider maintains access rules
- Common models: RBAC, ABAC, ACL
- Consider both action AND object in decisions
Critical: Object-Level Authorization
Always verify:
- Principal can perform this action type
- Principal can access this specific object
IDOR Prevention: Never skip object-level checks; verify principal has access to the specific objectId.
Security Considerations
Authentication Layer
- All session management best practices apply
- See: Opaque token-based authentication pattern
Authorization Layer
- Default deny: reject unless explicitly allowed
- Policy integrity: protect rules from tampering
- Complete mediation: check every request
Separation of Concerns
- Authentication determines WHO
- Authorization determines WHAT they can do
- Both must pass for action to proceed
Resource Protection
- Auth and Authz enforcers on critical path
- Potential DoS target—implement rate limiting
- Consider caching for performance
Session Data Security
- If storing sensitive data in session, encrypt it
- Minimize session data exposure
Implementation Checklist
- Secure session ID generation (128+ bits, CSPRNG)
- Session timeout policies (idle + absolute)
- New session ID on login
- Session invalidation on logout
- Authorization check on every request
- Object-level authorization (IDOR prevention)
- Default deny policy
- Policy integrity protection
- Rate limiting on enforcers
Related Patterns
- Opaque token-based authentication (session component)
- Authorisation (access control component)
- Limit request rate (DoS protection)
References
- Source: https://securitypatterns.distrinet-research.be/patterns/01_01_006__session_based_access_control/
- OWASP Session Management Cheat Sheet
- OWASP Authorization Cheat Sheet
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