Authorization Enforcer Pattern — Control Access After Authentication

In this tutorial, you'll learn how the Authorization Enforcer pattern controls what authenticated users can access based on roles.

What You'll Learn

how the Authorization Enforcer pattern controls what authenticated users can access based on roles.

Why It Matters

Authentication alone doesn't prevent unauthorized access. Authorization enforces granular permissions.

Real-World Use

RBAC with Spring Security, ASP.NET Core policies, and CASL in JavaScript.

The Authorization Enforcer Pattern

The Authorization Enforcer pattern addresses a specific recurring design problem by providing a reusable solution structure. Understanding when and how to apply it is essential for writing maintainable, scalable code.

Key Concepts

• Authentication: Verifying identity of request originators.
• Authorization: Determining what authenticated entities can access.
• Validation: Ensuring data conforms to expected formats.
• Audit: Logging security-relevant events for analysis.

Structure

The following diagram shows the structure of this pattern:

flowchart LR
    Request --> AuthorizationEnforcer
    AuthorizationEnforcer -->|pass| Handler
    AuthorizationEnforcer -->|block| Reject

Implementation

from typing import Optional
from dataclasses import dataclass
import re

@dataclass
class Request:
    path: str
    headers: dict
    body: str

class AuthorizationEnforcer:
    def __init__(self):
        self._blocked_patterns = [
            re.compile(r"<script>", re.I),
            re.compile(r"DROP TABLE", re.I),
            re.compile(r"../../etc/passwd"),
        ]

    def validate(self, request: Request) -> bool:
        for pattern in self._blocked_patterns:
            if pattern.search(request.body or ""):
                print(f"Blocked: malicious content in {request.path}")
                return False
            if pattern.search(str(request.headers)):
                print(f"Blocked: malicious headers in {request.path}")
                return False
        print(f"Passed: {request.path}")
        return True

validator = AuthorizationEnforcer()
reqs = [
    Request("/login", {}, "username=admin&password=1234"),
    Request("/search", {}, "q=<script>alert(1)</script>"),
    Request("/update", {"X-Forwarded-Host": "../../etc/passwd"}, "data=ok"),
]
for r in reqs:
    validator.validate(r)

Expected output:

Passed: /login
Blocked: malicious content in /search
Blocked: malicious headers in /update

Key Participants

• Client: Code that uses the Authorization Enforcer.
• Authorization Enforcer: The main abstraction provided by the pattern.
• Implementation: Concrete realization of the pattern.
• Data/State: Information managed by the pattern.

Real-World Examples

• DodaTech uses this pattern internally for consistent cross-cutting concerns.
• Major frameworks and libraries implement this pattern as a core architectural element.
• Production systems at scale depend on this pattern for reliability.

Related Patterns

• Authentication Enforcer

• Secure Service Proxy

• Intercepting Validator

• Design Patterns — the complete patterns catalog.

Pros and Cons

Common Mistakes

1. **Over-engineering: Applying Authorization Enforcer where a simpler solution suffices, adding unnecessary complexity.

2. **Wrong granularity: Implementing Authorization Enforcer at the wrong level of abstraction.

3. **Thread Safety ignored: Using Authorization Enforcer in concurrent context without proper synchronization.

4. **Tight coupling: Violating the pattern intent by creating hidden dependencies.

5. **Premature optimization: Introducing Authorization Enforcer before there is evidence it is needed.

Practice Questions

1. What problem does the Authorization Enforcer pattern solve? Describe a real-world scenario where using it improves code quality.

2. How does Authorization Enforcer differ from alternative approaches? What are the trade-offs?

3. What testing Strategy would you use for code that implements Authorization Enforcer?

4. How would you refactor legacy code to introduce Authorization Enforcer?

5. When should you NOT use Authorization Enforcer? Describe scenarios where it adds unnecessary complexity.

Challenge

Implement a complete Authorization Enforcer example in Python with unit tests. Include error handling, edge cases (empty data, null values, concurrent access), and a performance comparison against a simpler alternative. Document your design decisions.

Real-World Task

Find a section of code in your current project that could benefit from the Authorization Enforcer pattern. Refactor it, write tests, and measure the improvement in testability, coupling, and cohesion.

Security Tip: When implementing Authorization Enforcer, ensure proper input validation, avoid exposing internal state, and follow Least Privilege. At DodaTech, all implementations undergo security review.

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