Authorization Models Skill

Overview

This skill provides comprehensive guidance on authorization models and access control patterns. Authorization determines what authenticated users can do within a system.

Key Principle: Authorization should be declarative, centralized, and auditable.

When to Use This Skill

• Designing a permission system from scratch
• Choosing between RBAC, ABAC, ACL, or ReBAC
• Implementing policy-as-code with OPA
• Migrating from simple role checks to fine-grained authorization
• Implementing the principle of least privilege
• Designing multi-tenant authorization
• Building a Zanzibar-style permission system

Authorization Model Comparison

Model	Best For	Complexity	Scalability	Flexibility
ACL	File systems, simple resources	Low	Medium	Low
RBAC	Enterprise apps, clear job roles	Medium	High	Medium
ABAC	Complex policies, dynamic rules	High	High	High
ReBAC	Social graphs, document sharing	Medium-High	Very High	High

Quick Decision Tree

Need authorization model?
├── Simple resource ownership?
│   └── ACL (Access Control Lists)
├── Clear organizational roles?
│   └── RBAC (Role-Based Access Control)
├── Complex, context-dependent rules?
│   └── ABAC (Attribute-Based Access Control)
└── Relationship-based access (sharing, hierarchies)?
    └── ReBAC (Relationship-Based Access Control)

Role-Based Access Control (RBAC)

Core Concepts

/// <summary>
/// Fine-grained permissions for RBAC.
/// </summary>
[Flags]
public enum Permission
{
    None = 0,
    Read = 1,
    Create = 2,
    Update = 4,
    Delete = 8,
    Admin = 16,
    Approve = 32,
    Publish = 64,

    // Common combinations
    ReadWrite = Read | Update,
    Editor = Read | Create | Update,
    FullAccess = Read | Create | Update | Delete | Admin
}

/// <summary>
/// Role with associated permissions.
/// </summary>
public sealed record Role(string Name, Permission Permissions, string Description = "");

/// <summary>
/// Standard roles definition.
/// </summary>
public static class StandardRoles
{
    public static readonly Role Viewer = new("viewer", Permission.Read, "Read-only access");
    public static readonly Role Editor = new("editor", Permission.Editor, "Can create and edit content");
    public static readonly Role Admin = new("admin", Permission.FullAccess, "Full administrative access");

    public static readonly IReadOnlyDictionary<string, Role> All = new Dictionary<string, Role>
    {
        [Viewer.Name] = Viewer,
        [Editor.Name] = Editor,
        [Admin.Name] = Admin
    };
}

RBAC Implementation

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;

/// <summary>
/// Simple RBAC authorization service.
/// </summary>
public sealed class RbacAuthorizer
{
    private readonly Dictionary<string, HashSet<string>> _userRoles = new();

    public void AssignRole(string userId, string role)
    {
        if (!_userRoles.TryGetValue(userId, out var roles))
        {
            roles = new HashSet<string>();
            _userRoles[userId] = roles;
        }
        roles.Add(role);
    }

    public bool HasPermission(string userId, Permission permission)
    {
        if (!_userRoles.TryGetValue(userId, out var userRoles))
            return false;

        foreach (var roleName in userRoles)
        {
            if (StandardRoles.All.TryGetValue(roleName, out var role) &&
                role.Permissions.HasFlag(permission))
            {
                return true;
            }
        }
        return false;
    }

    public bool HasRole(string userId, string role) =>
        _userRoles.TryGetValue(userId, out var roles) && roles.Contains(role);
}

/// <summary>
/// ASP.NET Core authorization requirement for permissions.
/// </summary>
public sealed class PermissionRequirement(Permission permission) : IAuthorizationRequirement
{
    public Permission Permission { get; } = permission;
}

/// <summary>
/// Handler for permission-based authorization.
/// </summary>
public sealed class PermissionHandler(RbacAuthorizer authorizer) : AuthorizationHandler<PermissionRequirement>
{
    protected override Task HandleRequirementAsync(
        AuthorizationHandlerContext context,
        PermissionRequirement requirement)
    {
        var userId = context.User.FindFirstValue(ClaimTypes.NameIdentifier);
        if (userId is not null && authorizer.HasPermission(userId, requirement.Permission))
        {
            context.Succeed(requirement);
        }
        return Task.CompletedTask;
    }
}

// Usage with attribute
[Authorize(Policy = "RequireCreate")]
[HttpPost("articles")]
public IActionResult CreateArticle([FromBody] ArticleDto article)
{
    // Only users with CREATE permission can access
    return Ok();
}

Hierarchical RBAC

/// <summary>
/// Role with inheritance support.
/// </summary>
public sealed class HierarchicalRole(
    string name,
    Permission directPermissions,
    HierarchicalRole? parent = null)
{
    public string Name { get; } = name;
    public HierarchicalRole? Parent { get; } = parent;

    /// <summary>
    /// Get all permissions including inherited from parent roles.
    /// </summary>
    public Permission AllPermissions
    {
        get
        {
            var permissions = directPermissions;
            var current = Parent;
            while (current is not null)
            {
                permissions |= current.AllPermissions;
                current = current.Parent;
            }
            return permissions;
        }
    }
}

// Role hierarchy: admin > editor > viewer
var viewerRole = new HierarchicalRole("viewer", Permission.Read);
var editorRole = new HierarchicalRole("editor", Permission.Create | Permission.Update, viewerRole);
var adminRole = new HierarchicalRole("admin", Permission.Delete | Permission.Admin, editorRole);

// adminRole.AllPermissions includes all permissions from parent roles

Attribute-Based Access Control (ABAC)

Core Concepts

using System.Collections.Immutable;

/// <summary>
/// Context for an access decision.
/// </summary>
public sealed record AccessRequest(
    ImmutableDictionary<string, object> Subject,     // Who is requesting
    ImmutableDictionary<string, object> Resource,    // What they're accessing
    string Action,                                    // What they want to do
    ImmutableDictionary<string, object> Environment  // Context (time, location, etc.)
)
{
    public T GetSubjectAttribute<T>(string key, T defaultValue = default!) =>
        Subject.TryGetValue(key, out var value) && value is T typed ? typed : defaultValue;

    public T GetResourceAttribute<T>(string key, T defaultValue = default!) =>
        Resource.TryGetValue(key, out var value) && value is T typed ? typed : defaultValue;

    public T GetEnvironmentAttribute<T>(string key, T defaultValue = default!) =>
        Environment.TryGetValue(key, out var value) && value is T typed ? typed : defaultValue;
}

/// <summary>
/// Policy effect type.
/// </summary>
public enum PolicyEffect { Permit, Deny }

/// <summary>
/// Attribute-based policy evaluation.
/// </summary>
public sealed class AbacPolicy(
    string name,
    Func<AccessRequest, bool> condition,
    PolicyEffect effect = PolicyEffect.Permit)
{
    public string Name { get; } = name;

    /// <summary>
    /// Return effect if condition matches, null otherwise.
    /// </summary>
    public PolicyEffect? Evaluate(AccessRequest request) =>
        condition(request) ? effect : null;
}

ABAC Policy Examples

// Policy: Only managers can approve expenses over $1000
var managerApprovalPolicy = new AbacPolicy(
    name: "manager_approval",
    condition: req =>
        req.Action == "approve" &&
        req.GetResourceAttribute<string>("type") == "expense" &&
        req.GetResourceAttribute<decimal>("amount") > 1000 &&
        req.GetSubjectAttribute<string>("role") == "manager"
);

// Policy: Users can only access their own department's data
var departmentIsolationPolicy = new AbacPolicy(
    name: "department_isolation",
    condition: req =>
        req.GetSubjectAttribute<string>("department") ==
        req.GetResourceAttribute<string>("department")
);

// Policy: No access outside business hours
var businessHoursPolicy = new AbacPolicy(
    name: "business_hours",
    condition: req =>
    {
        var now = DateTime.Now;
        var hour = now.Hour;
        var dayOfWeek = now.DayOfWeek;
        return hour >= 9 && hour <= 17 &&
               dayOfWeek != DayOfWeek.Saturday &&
               dayOfWeek != DayOfWeek.Sunday;
    }
);

// Policy: Deny access from untrusted networks
var networkPolicy = new AbacPolicy(
    name: "trusted_network",
    condition: req =>
        req.GetEnvironmentAttribute<string>("ip_address", "")
           .StartsWith("10.0.", StringComparison.Ordinal)
);

ABAC Policy Engine

/// <summary>
/// Policy decision point (PDP) with deny-overrides algorithm.
/// </summary>
public sealed class AbacEngine(PolicyEffect defaultEffect = PolicyEffect.Deny)
{
    private readonly List<AbacPolicy> _policies = [];

    public void AddPolicy(AbacPolicy policy) => _policies.Add(policy);

    /// <summary>
    /// Evaluate all policies. Deny-overrides combining algorithm.
    /// </summary>
    public bool Evaluate(AccessRequest request)
    {
        var permitFound = false;

        foreach (var policy in _policies)
        {
            var effect = policy.Evaluate(request);
            if (effect == PolicyEffect.Deny)
            {
                return false;  // Explicit deny always wins
            }
            if (effect == PolicyEffect.Permit)
            {
                permitFound = true;
            }
        }

        return permitFound || defaultEffect == PolicyEffect.Permit;
    }
}

// Usage
var engine = new AbacEngine();
engine.AddPolicy(departmentIsolationPolicy);
engine.AddPolicy(businessHoursPolicy);

var request = new AccessRequest(
    Subject: ImmutableDictionary.CreateRange(new Dictionary<string, object>
    {
        ["user_id"] = "123",
        ["department"] = "engineering",
        ["role"] = "developer"
    }),
    Resource: ImmutableDictionary.CreateRange(new Dictionary<string, object>
    {
        ["id"] = "doc-456",
        ["department"] = "engineering",
        ["type"] = "document"
    }),
    Action: "read",
    Environment: ImmutableDictionary.CreateRange(new Dictionary<string, object>
    {
        ["ip_address"] = "10.0.1.50",
        ["time"] = DateTime.UtcNow
    })
);

if (engine.Evaluate(request))
{
    // Access granted
}

Access Control Lists (ACL)

Simple ACL Implementation

/// <summary>
/// Unix-style ACL permissions.
/// </summary>
[Flags]
public enum AclPermission
{
    None = 0,
    Read = 1,
    Write = 2,
    Execute = 4,
    Delete = 8,
    Admin = 16,

    // Common combinations
    ReadWrite = Read | Write,
    Full = Read | Write | Execute | Delete | Admin
}

/// <summary>
/// Principal type for ACL entries.
/// </summary>
public enum PrincipalType { User, Group }

/// <summary>
/// Access control entry.
/// </summary>
public sealed class AclEntry(string principal, AclPermission permissions, PrincipalType principalType = PrincipalType.User)
{
    public string Principal { get; } = principal;
    public AclPermission Permissions { get; set; } = permissions;
    public PrincipalType PrincipalType { get; } = principalType;
}

/// <summary>
/// Access control list for a resource.
/// </summary>
public sealed class Acl(string resourceId, string owner)
{
    public string ResourceId { get; } = resourceId;
    public string Owner { get; } = owner;
    private readonly Dictionary<string, AclEntry> _entries = new();

    /// <summary>
    /// Grant permissions to a principal.
    /// </summary>
    public void Grant(string principal, AclPermission permissions, PrincipalType principalType = PrincipalType.User)
    {
        if (_entries.TryGetValue(principal, out var entry))
        {
            entry.Permissions |= permissions;
        }
        else
        {
            _entries[principal] = new AclEntry(principal, permissions, principalType);
        }
    }

    /// <summary>
    /// Revoke permissions from a principal.
    /// </summary>
    public void Revoke(string principal, AclPermission permissions)
    {
        if (_entries.TryGetValue(principal, out var entry))
        {
            entry.Permissions &= ~permissions;
            if (entry.Permissions == AclPermission.None)
            {
                _entries.Remove(principal);
            }
        }
    }

    /// <summary>
    /// Check if principal has permission.
    /// </summary>
    public bool Check(string principal, AclPermission permission, ISet<string>? userGroups = null)
    {
        // Owner has full access
        if (principal == Owner)
        {
            return true;
        }

        // Check direct user entry
        if (_entries.TryGetValue(principal, out var entry) &&
            entry.Permissions.HasFlag(permission))
        {
            return true;
        }

        // Check group entries
        if (userGroups is not null)
        {
            foreach (var group in userGroups)
            {
                if (_entries.TryGetValue(group, out var groupEntry) &&
                    groupEntry.PrincipalType == PrincipalType.Group &&
                    groupEntry.Permissions.HasFlag(permission))
                {
                    return true;
                }
            }
        }

        return false;
    }
}

ACL Usage Example

// Create ACL for a document
var docAcl = new Acl(resourceId: "doc-123", owner: "alice");

// Grant permissions
docAcl.Grant("bob", AclPermission.ReadWrite);
docAcl.Grant("engineering", AclPermission.Read, PrincipalType.Group);
docAcl.Grant("charlie", AclPermission.Read);

// Check permissions
docAcl.Check("alice", AclPermission.Delete);   // True (owner)
docAcl.Check("bob", AclPermission.Write);      // True (explicit grant)
docAcl.Check("bob", AclPermission.Delete);     // False (not granted)
docAcl.Check("dave", AclPermission.Read,
             userGroups: new HashSet<string> { "engineering" });  // True (group membership)

Relationship-Based Access Control (ReBAC)

Zanzibar-Style Model

/// <summary>
/// A relationship tuple (object, relation, subject) in Zanzibar style.
/// </summary>
public readonly record struct Relationship(
    string ObjectType,
    string ObjectId,
    string Relation,
    string SubjectType,
    string SubjectId,
    string? SubjectRelation = null)  // For usersets
{
    public override string ToString()
    {
        var subject = $"{SubjectType}:{SubjectId}";
        if (SubjectRelation is not null)
        {
            subject += $"#{SubjectRelation}";
        }
        return $"{ObjectType}:{ObjectId}#{Relation}@{subject}";
    }
}

/// <summary>
/// Simple ReBAC implementation (Zanzibar-inspired).
/// </summary>
public sealed class ReBac
{
    // Store relationships: (object_type, object_id, relation) -> set of subjects
    private readonly Dictionary<(string ObjectType, string ObjectId, string Relation),
                                HashSet<(string SubjectType, string SubjectId, string? SubjectRelation)>> _tuples = new();

    // Relation definitions with computed relations
    // object_type -> relation -> set of parent relations for inheritance
    private readonly Dictionary<string, Dictionary<string, HashSet<string>>> _relationConfig = new();

    /// <summary>
    /// Define a relation and its inheritance.
    /// </summary>
    public void DefineRelation(string objectType, string relation, IEnumerable<string>? inheritsFrom = null)
    {
        if (!_relationConfig.TryGetValue(objectType, out var relations))
        {
            relations = new Dictionary<string, HashSet<string>>();
            _relationConfig[objectType] = relations;
        }
        relations[relation] = inheritsFrom?.ToHashSet() ?? [];
    }

    /// <summary>
    /// Write a relationship tuple.
    /// </summary>
    public void Write(Relationship rel)
    {
        var key = (rel.ObjectType, rel.ObjectId, rel.Relation);
        if (!_tuples.TryGetValue(key, out var subjects))
        {
            subjects = [];
            _tuples[key] = subjects;
        }
        subjects.Add((rel.SubjectType, rel.SubjectId, rel.SubjectRelation));
    }

    /// <summary>
    /// Delete a relationship tuple.
    /// </summary>
    public void Delete(Relationship rel)
    {
        var key = (rel.ObjectType, rel.ObjectId, rel.Relation);
        if (_tuples.TryGetValue(key, out var subjects))
        {
            subjects.Remove((rel.SubjectType, rel.SubjectId, rel.SubjectRelation));
        }
    }

    /// <summary>
    /// Check if subject has relation to object.
    /// </summary>
    public bool Check(string objectType, string objectId, string relation,
                      string subjectType, string subjectId)
    {
        var key = (objectType, objectId, relation);

        // Direct check
        if (_tuples.TryGetValue(key, out var subjects) &&
            subjects.Contains((subjectType, subjectId, null)))
        {
            return true;
        }

        // Check inherited relations
        if (_relationConfig.TryGetValue(objectType, out var relations) &&
            relations.TryGetValue(relation, out var inherited))
        {
            foreach (var parentRelation in inherited)
            {
                if (Check(objectType, objectId, parentRelation, subjectType, subjectId))
                {
                    return true;
                }
            }
        }

        // Check userset rewrite (e.g., folder:123#viewer@document:456#parent)
        if (_tuples.TryGetValue(key, out var tupleSubjects))
        {
            foreach (var (subjType, subjId, subjRel) in tupleSubjects)
            {
                if (subjRel is not null)
                {
                    // This is a userset - check if user has that relation on referenced object
                    if (Check(subjType, subjId, subjRel, subjectType, subjectId))
                    {
                        return true;
                    }
                }
            }
        }

        return false;
    }
}

ReBAC Usage Example (Google Drive-style)

// Initialize ReBAC
var rebac = new ReBac();

// Define relation hierarchy
// Editors can also view (editor inherits from viewer)
rebac.DefineRelation("document", "viewer", null);
rebac.DefineRelation("document", "editor", ["viewer"]);
rebac.DefineRelation("document", "owner", ["editor"]);

rebac.DefineRelation("folder", "viewer", null);
rebac.DefineRelation("folder", "editor", ["viewer"]);
rebac.DefineRelation("folder", "owner", ["editor"]);

// folder viewers are document viewers (documents inherit from parent folder)
rebac.DefineRelation("document", "parent", null);

// Create relationships
// Alice owns folder "projects"
rebac.Write(new Relationship("folder", "projects", "owner", "user", "alice"));

// Bob is an editor on folder "projects"
rebac.Write(new Relationship("folder", "projects", "editor", "user", "bob"));

// Document "spec" is in folder "projects"
// Anyone who can view the folder can view the document
rebac.Write(new Relationship("document", "spec", "parent", "folder", "projects",
                             SubjectRelation: "viewer"));

// Charlie has direct viewer access to document
rebac.Write(new Relationship("document", "spec", "viewer", "user", "charlie"));

// Check permissions
rebac.Check("folder", "projects", "owner", "user", "alice");    // True
rebac.Check("folder", "projects", "viewer", "user", "alice");   // True (owner->editor->viewer)
rebac.Check("folder", "projects", "editor", "user", "bob");     // True
rebac.Check("document", "spec", "viewer", "user", "bob");       // True (folder editor->viewer)
rebac.Check("document", "spec", "editor", "user", "charlie");   // False (only viewer)

Policy-as-Code with Open Policy Agent (OPA)

Rego Policy Basics

# policy.rego
package authz

import future.keywords.if
import future.keywords.in

# Default deny
default allow := false

# Allow if user has required permission
allow if {
    user_has_permission[input.action]
}

# User permissions based on roles
user_has_permission[permission] if {
    some role in input.user.roles
    some permission in role_permissions[role]
}

# Role to permission mapping
role_permissions := {
    "admin": ["read", "write", "delete", "admin"],
    "editor": ["read", "write"],
    "viewer": ["read"],
}

# Resource-specific rules
allow if {
    input.action == "read"
    input.resource.public == true
}

# Owner can always access their resources
allow if {
    input.resource.owner == input.user.id
}

OPA Integration in .NET

using System.Text.Json;
using System.Text.Json.Serialization;

/// <summary>
/// Client for Open Policy Agent.
/// </summary>
public sealed class OpaClient(HttpClient httpClient, string opaUrl = "http://localhost:8181") : IDisposable
{
    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
    };

    /// <summary>
    /// Query OPA for a policy decision.
    /// </summary>
    public async Task<bool> CheckAsync(string policyPath, object inputData, CancellationToken cancellationToken = default)
    {
        var url = $"{opaUrl}/v1/data/{policyPath}";
        var request = new OpaRequest(inputData);

        var response = await httpClient.PostAsJsonAsync(url, request, JsonOptions, cancellationToken);
        response.EnsureSuccessStatusCode();

        var result = await response.Content.ReadFromJsonAsync<OpaResponse<bool>>(JsonOptions, cancellationToken);
        return result?.Result ?? false;
    }

    /// <summary>
    /// Run an arbitrary Rego query.
    /// </summary>
    public async Task<JsonElement?> QueryAsync(string query, object inputData, CancellationToken cancellationToken = default)
    {
        var url = $"{opaUrl}/v1/query";
        var request = new { query, input = inputData };

        var response = await httpClient.PostAsJsonAsync(url, request, JsonOptions, cancellationToken);
        response.EnsureSuccessStatusCode();

        var result = await response.Content.ReadFromJsonAsync<OpaResponse<JsonElement>>(JsonOptions, cancellationToken);
        return result?.Result;
    }

    public void Dispose() => httpClient.Dispose();

    private sealed record OpaRequest([property: JsonPropertyName("input")] object Input);
    private sealed record OpaResponse<T>([property: JsonPropertyName("result")] T? Result);
}

// Usage
using var httpClient = new HttpClient();
var opa = new OpaClient(httpClient);

var inputData = new
{
    user = new
    {
        id = "alice",
        roles = new[] { "editor" }
    },
    action = "write",
    resource = new
    {
        id = "doc-123",
        owner = "bob",
        @public = false
    }
};

if (await opa.CheckAsync("authz/allow", inputData))
{
    // Access granted
}

OPA with ABAC Policies

# abac_policy.rego
package abac

import future.keywords.if
import future.keywords.in

default allow := false

# Time-based access
allow if {
    input.action == "read"
    is_business_hours
    user_in_same_department
}

is_business_hours if {
    time.hour(time.now_ns()) >= 9
    time.hour(time.now_ns()) <= 17
    time.weekday(time.now_ns()) < 5
}

user_in_same_department if {
    input.user.department == input.resource.department
}

# Expense approval rules
allow if {
    input.action == "approve"
    input.resource.type == "expense"
    can_approve_amount
}

can_approve_amount if {
    input.resource.amount <= 1000
    "employee" in input.user.roles
}

can_approve_amount if {
    input.resource.amount <= 10000
    "manager" in input.user.roles
}

can_approve_amount if {
    "director" in input.user.roles
}

Authorization Libraries and Tools

Comparison

Tool	Model	Language	Best For
OPA	ABAC/Policy	Rego	Kubernetes, microservices
Casbin	RBAC/ABAC/ACL	Multi-language	General purpose
Oso	ABAC/ReBAC	Polar	Application embedding
SpiceDB	ReBAC (Zanzibar)	gRPC	Large-scale permissions
Cerbos	ABAC	YAML	Cloud-native apps

Casbin Quick Start

using Casbin;

// Define model (model.conf)
/*
[request_definition]
r = sub, obj, act

[policy_definition]
p = sub, obj, act

[role_definition]
g = _, _

[policy_effect]
e = some(where (p.eft == allow))

[matchers]
m = g(r.sub, p.sub) && r.obj == p.obj && r.act == p.act
*/

// Create enforcer
var enforcer = new Enforcer("model.conf", "policy.csv");

// Check permission
if (enforcer.Enforce("alice", "data1", "read"))
{
    // Access granted
}

// Add policy dynamically
await enforcer.AddPolicyAsync("bob", "data2", "write");
await enforcer.AddGroupingPolicyAsync("alice", "admin");

// For ASP.NET Core integration, use Casbin.AspNetCore
// services.AddCasbinAuthorization(options =>
// {
//     options.DefaultModelPath = "model.conf";
//     options.DefaultPolicyPath = "policy.csv";
// });

Best Practices

Design Principles

1. Principle of Least Privilege: Grant minimum permissions necessary
2. Separation of Duties: Require multiple parties for sensitive operations
3. Defense in Depth: Layer authorization checks at multiple levels
4. Fail Secure: Deny access when authorization state is unclear
5. Centralize Logic: Single policy decision point (PDP)
6. Audit Everything: Log all authorization decisions

Implementation Guidelines

// Good: Centralized authorization
public interface IAuditLogger
{
    Task LogAsync(string userId, string resourceId, string action, string decision, object? context);
}

/// <summary>
/// Centralized authorization service - single entry point for all decisions.
/// </summary>
public sealed class AuthorizationService(AbacEngine engine, IAuditLogger auditLogger)
{
    /// <summary>
    /// Single entry point for all authorization decisions.
    /// </summary>
    public async Task<bool> AuthorizeAsync(AccessRequest request)
    {
        var decision = engine.Evaluate(request);

        // Always audit
        await auditLogger.LogAsync(
            userId: request.GetSubjectAttribute<string>("user_id") ?? "unknown",
            resourceId: request.GetResourceAttribute<string>("id") ?? "unknown",
            action: request.Action,
            decision: decision ? "permit" : "deny",
            context: request.Environment
        );

        return decision;
    }
}

// Bad: Scattered authorization checks
public Document? GetDocument(string docId, User user)
{
    var doc = _repository.GetById(docId);
    // Authorization logic duplicated everywhere - avoid this pattern!
    if (user.Role == "admin" || doc?.OwnerId == user.Id)
    {
        return doc;
    }
    return null;
}

Common Pitfalls

Pitfall	Problem	Solution
Hardcoded roles	Inflexible, hard to change	Use permission-based checks
Missing negative tests	False sense of security	Test deny cases explicitly
Client-side only	Easily bypassed	Always enforce server-side
Overly complex policies	Hard to audit	Keep policies simple, composable
No audit trail	Can't investigate incidents	Log all decisions

Related Skills

• authentication-patterns - Verify identity before authorization
• api-security - Apply authorization at API boundaries
• zero-trust - Never trust, always verify architecture
• secure-coding - Prevent authorization bypass vulnerabilities

References

Deep Dives:

• RBAC Patterns - Advanced RBAC with constraints
• ABAC Implementation - Full XACML-style engine
• Policy-as-Code - OPA, Cerbos, and testing patterns

Security Checklist

Design Phase

• Authorization model chosen based on requirements
• Principle of least privilege applied
• Roles/permissions documented
• Edge cases identified (inheritance, delegation)

Implementation Phase

• Authorization centralized (single PDP)
• Server-side enforcement
• Consistent authorization checks on all endpoints
• Audit logging implemented

Testing Phase

• Positive tests (allowed access works)
• Negative tests (denied access blocked)
• Privilege escalation tests
• Role hierarchy tests

Operations Phase

• Regular permission reviews
• Unused roles/permissions removed
• Audit logs monitored
• Incident response plan for auth failures