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Okay, let's create a design document for the MediatR library, focusing on its use within a larger system and addressing security considerations.

BUSINESS POSTURE

Business Priorities and Goals:

MediatR, as a library, doesn't directly address business problems. Instead, it facilitates a specific architectural pattern (mediator pattern) that aims to:

  • Reduce direct dependencies between different parts of an application.
  • Improve code maintainability and testability by decoupling request handling logic.
  • Promote a cleaner separation of concerns.
  • Simplify complex workflows by breaking them down into smaller, manageable units.

The business goals achieved by using MediatR are therefore indirect and relate to software development best practices:

  • Faster development cycles (due to improved maintainability).
  • Reduced risk of bugs (due to better testability and separation of concerns).
  • Easier onboarding of new developers (due to a more structured codebase).
  • More adaptable code that can respond to changing business requirements.

Most Important Business Risks:

  • Incorrect Implementation: If MediatR is misused (e.g., handlers become overly complex, the mediator itself becomes a bottleneck), it can negate its benefits and introduce new problems. This is a development process risk.
  • Over-Engineering: For very simple applications, using MediatR might be overkill, adding unnecessary complexity. This is a design risk.
  • Dependency Management: Although MediatR itself has minimal external dependencies, the overall application using it will have its own set of dependencies. Managing these dependencies securely is crucial. This is a supply chain risk.
  • Security Vulnerabilities in Handlers: The code within the request handlers is where the actual business logic resides. Vulnerabilities here are the primary security concern, and MediatR itself doesn't inherently mitigate these. This is an application security risk.

SECURITY POSTURE

Existing Security Controls (as inferred from the library and common usage patterns):

  • security control: Dependency Management: The library itself has few dependencies, reducing the attack surface from external libraries. (Refer to the .csproj file in the repository).
  • security control: Code Simplicity: The core MediatR library is relatively small and focused, making it easier to audit and understand. (Review the source code in the repository).
  • security control: Promotes Testability: The design encourages writing unit tests for individual handlers, which can help catch security flaws early. (Testing is a general development practice, not explicitly enforced by MediatR).

Accepted Risks:

  • accepted risk: Handler Vulnerabilities: MediatR does not perform any input validation, output encoding, or authorization checks within the library itself. These are the responsibility of the developer implementing the handlers.
  • accepted risk: Asynchronous Processing Risks: If using asynchronous handlers, developers must be aware of potential issues like race conditions, deadlocks, and exception handling in asynchronous contexts.
  • accepted risk: Over-reliance on Mediator: Developers might be tempted to put too much logic into the mediator itself or create overly complex handler chains, leading to performance or maintainability issues.

Recommended Security Controls (High Priority):

  • security control: Input Validation: Implement robust input validation in every request handler to prevent common vulnerabilities like injection attacks (SQL injection, command injection, XSS).
  • security control: Output Encoding: Ensure proper output encoding is used when data is rendered to prevent XSS vulnerabilities. This is particularly relevant if handlers are used in web applications.
  • security control: Authorization: Implement authorization checks within handlers to ensure that users have the necessary permissions to perform the requested actions.
  • security control: Secure Configuration Management: If handlers rely on configuration settings (e.g., database connection strings, API keys), these should be stored and managed securely.
  • security control: Logging and Monitoring: Implement comprehensive logging and monitoring to detect and respond to security incidents. Log relevant events within handlers, and monitor for unusual activity.
  • security control: Dependency Scanning: Regularly scan all project dependencies (including MediatR and any libraries used within handlers) for known vulnerabilities.
  • security control: Static Code Analysis: Integrate static code analysis tools (SAST) into the development pipeline to identify potential security flaws in handlers.

Security Requirements:

  • Authentication: MediatR itself does not handle authentication. Authentication should be handled before a request reaches the mediator. This is typically done at the application's entry point (e.g., API controller, web page).
  • Authorization: Authorization checks should be performed within the relevant request handlers. Each handler should verify that the authenticated user (or system) has the necessary permissions to execute the requested operation.
  • Input Validation: Every request handler should validate all input data it receives. This includes checking data types, lengths, formats, and allowed values. Use a whitelist approach whenever possible (define what is allowed, reject everything else).
  • Cryptography: If handlers need to perform cryptographic operations (e.g., hashing passwords, encrypting data), they should use well-established cryptographic libraries and follow best practices (e.g., using appropriate key lengths, secure random number generators, avoiding deprecated algorithms). MediatR itself does not provide cryptographic functionality.
  • Error Handling: Handlers should handle errors gracefully and avoid leaking sensitive information in error messages.

DESIGN

C4 CONTEXT

graph LR
    User["User (Web Browser/Mobile App/Other Client)"] -- "Makes requests" --> System["System using MediatR"];
    System -- "Uses" --> MediatR["MediatR Library"];
    System -- "Interacts with" --> ExternalSystem1["External System 1 (e.g., Database)"];
    System -- "Interacts with" --> ExternalSystem2["External System 2 (e.g., Third-party API)"];
    System -- "Interacts with" --> ExternalSystem3["External System 3 (e.g., Message Queue)"];
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C4 Context Element List:

  • Element:

    • Name: User
    • Type: Person
    • Description: Represents any user or client application interacting with the system.
    • Responsibilities: Initiates requests to the system.
    • Security Controls: Authentication mechanisms (e.g., OAuth, JWT, API keys) at the system boundary.

  • Element:

    • Name: System using MediatR
    • Type: Software System
    • Description: The overall application or system that utilizes the MediatR library for internal request handling.
    • Responsibilities: Processes user requests, orchestrates business logic, interacts with external systems.
    • Security Controls: Input validation, output encoding, authorization, secure configuration management, logging and monitoring, error handling.

  • Element:

    • Name: MediatR Library
    • Type: Library
    • Description: The MediatR library itself, providing the mediator pattern implementation.
    • Responsibilities: Facilitates communication between request senders and handlers.
    • Security Controls: Limited attack surface due to small codebase and few dependencies.

  • Element:

    • Name: External System 1 (e.g., Database)
    • Type: Software System
    • Description: An external system, such as a database, that the main system interacts with.
    • Responsibilities: Stores and retrieves data.
    • Security Controls: Database security best practices (e.g., access control, encryption, auditing).

  • Element:

    • Name: External System 2 (e.g., Third-party API)
    • Type: Software System
    • Description: An external system, such as a third-party API, that the main system interacts with.
    • Responsibilities: Provides specific services or data.
    • Security Controls: Secure API communication (e.g., HTTPS, API keys, rate limiting).

  • Element:

    • Name: External System 3 (e.g., Message Queue)
    • Type: Software System
    • Description: An external system, such as a message queue, that the main system interacts with.
    • Responsibilities: Asynchronous message processing.
    • Security Controls: Secure message queue configuration (e.g., access control, encryption).

C4 CONTAINER

graph LR
    User["User"] -- "Makes requests" --> WebAPI["Web API (e.g., ASP.NET Core)"];
    WebAPI -- "Sends requests" --> Mediator["Mediator (MediatR)"];
    Mediator -- "Dispatches to" --> Handler1["Request Handler 1"];
    Mediator -- "Dispatches to" --> Handler2["Request Handler 2"];
    Handler1 -- "Uses" --> Repository1["Repository 1"];
    Handler2 -- "Uses" --> Service1["External Service Client"];
    Repository1 -- "Accesses" --> Database["Database"];
    Service1 -- "Calls" --> ExternalAPI["External API"];
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C4 Container Element List:

  • Element:

    • Name: User
    • Type: Person
    • Description: Represents any user or client application interacting with the system.
    • Responsibilities: Initiates requests to the system.
    • Security Controls: Authentication mechanisms (e.g., OAuth, JWT, API keys) at the Web API.

  • Element:

    • Name: Web API (e.g., ASP.NET Core)
    • Type: Container (Web Application)
    • Description: The entry point for external requests. Handles routing, authentication, and initial request processing.
    • Responsibilities: Receives requests, authenticates users, forwards requests to the Mediator.
    • Security Controls: Authentication, input validation (initial), rate limiting, TLS/HTTPS.

  • Element:

    • Name: Mediator (MediatR)
    • Type: Container (Component)
    • Description: The MediatR mediator instance. Receives requests and dispatches them to the appropriate handlers.
    • Responsibilities: Routes requests to handlers based on request type.
    • Security Controls: None directly within MediatR; relies on security controls in Web API and Handlers.

  • Element:

    • Name: Request Handler 1
    • Type: Container (Component)
    • Description: A class that handles a specific type of request. Contains business logic.
    • Responsibilities: Processes a specific request, interacts with repositories or other services.
    • Security Controls: Input validation, authorization, output encoding (if applicable), error handling.

  • Element:

    • Name: Request Handler 2
    • Type: Container (Component)
    • Description: Another class that handles a different type of request.
    • Responsibilities: Processes a specific request, interacts with repositories or other services.
    • Security Controls: Input validation, authorization, output encoding (if applicable), error handling.

  • Element:

    • Name: Repository 1
    • Type: Container (Component)
    • Description: A class that handles data access for a specific entity or data source.
    • Responsibilities: Retrieves and persists data to the database.
    • Security Controls: Parameterized queries (to prevent SQL injection), data validation.

  • Element:

    • Name: Service 1
    • Type: Container (Component)
    • Description: A class that handles communication with an external service.
    • Responsibilities: Makes requests to the External API.
    • Security Controls: Secure API communication (HTTPS, API keys), input validation, error handling.

  • Element:

    • Name: Database
    • Type: Container (Database)
    • Description: The database used by the application.
    • Responsibilities: Stores and retrieves data.
    • Security Controls: Database security best practices (access control, encryption, auditing).

  • Element:

    • Name: External API
    • Type: Container (External System)
    • Description: A third-party API used by the application.
    • Responsibilities: Provides specific services or data.
    • Security Controls: Managed by the third-party provider; the application should use secure communication (HTTPS, API keys).

DEPLOYMENT

Possible Deployment Solutions:

  1. Cloud-Based (e.g., Azure App Service, AWS Elastic Beanstalk, Google App Engine): The application is packaged and deployed as a web application to a managed cloud platform.
  2. Containerized (e.g., Docker, Kubernetes): The application is containerized using Docker and deployed to a container orchestration platform like Kubernetes.
  3. Virtual Machine (e.g., Azure VM, AWS EC2): The application is deployed to a virtual machine running a web server (e.g., IIS, Nginx).
  4. On-Premise Server: The application is deployed to a physical or virtual server within the organization's own data center.

Chosen Solution (for detailed description): Containerized (Docker & Kubernetes)

graph LR
    DevMachine["Developer Machine"] -- "Builds & Pushes" --> ContainerRegistry["Container Registry (e.g., Docker Hub, ACR, ECR)"];
    ContainerRegistry -- "Provides Image" --> KubernetesCluster["Kubernetes Cluster"];
    KubernetesCluster -- "Runs" --> Pod1["Pod (App Instance 1)"];
    KubernetesCluster -- "Runs" --> Pod2["Pod (App Instance 2)"];
    Pod1 -- "Uses" --> DatabaseInstance["Database Instance"];
    Pod2 -- "Uses" --> DatabaseInstance;
    LoadBalancer["Load Balancer"] -- "Routes traffic" --> KubernetesCluster;
    User -- "Accesses" --> LoadBalancer;
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Deployment Element List:

  • Element:

    • Name: Developer Machine
    • Type: Infrastructure Node
    • Description: The developer's workstation where code is written and built.
    • Responsibilities: Code development, building Docker images.
    • Security Controls: Local development environment security (e.g., firewall, antivirus).

  • Element:

    • Name: Container Registry (e.g., Docker Hub, ACR, ECR)
    • Type: Infrastructure Node
    • Description: A repository for storing and managing Docker images.
    • Responsibilities: Stores Docker images, provides images to the Kubernetes cluster.
    • Security Controls: Access control, image scanning for vulnerabilities.

  • Element:

    • Name: Kubernetes Cluster
    • Type: Infrastructure Node
    • Description: The Kubernetes cluster where the application is deployed.
    • Responsibilities: Orchestrates container deployment, scaling, and management.
    • Security Controls: Kubernetes security best practices (e.g., RBAC, network policies, pod security policies).

  • Element:

    • Name: Pod (App Instance 1)
    • Type: Infrastructure Node
    • Description: A running instance of the application container.
    • Responsibilities: Executes the application code.
    • Security Controls: Container security best practices (e.g., minimal base image, non-root user).

  • Element:

    • Name: Pod (App Instance 2)
    • Type: Infrastructure Node
    • Description: Another running instance of the application container (for scaling and redundancy).
    • Responsibilities: Executes the application code.
    • Security Controls: Container security best practices (e.g., minimal base image, non-root user).

  • Element:

    • Name: Database Instance
    • Type: Infrastructure Node
    • Description: The database instance used by the application.
    • Responsibilities: Stores and retrieves data.
    • Security Controls: Database security best practices (access control, encryption, auditing).

  • Element:

    • Name: Load Balancer
    • Type: Infrastructure Node
    • Description: Distributes incoming traffic across multiple application instances.
    • Responsibilities: Load balancing, SSL termination (potentially).
    • Security Controls: Secure configuration, DDoS protection (potentially).

  • Element:

    • Name: User
    • Type: Person
    • Description: User accessing application.
    • Responsibilities: Access application.
    • Security Controls: Authentication.

BUILD

graph LR
    Developer["Developer"] -- "Commits code" --> GitRepository["Git Repository (e.g., GitHub, GitLab)"];
    GitRepository -- "Triggers" --> CI_CD["CI/CD Pipeline (e.g., GitHub Actions, Jenkins)"];
    CI_CD -- "Runs tests" --> TestEnvironment["Test Environment"];
    CI_CD -- "Performs SAST" --> SAST_Scanner["SAST Scanner"];
    CI_CD -- "Performs Dependency Check" --> DependencyChecker["Dependency Checker"];
    CI_CD -- "Builds" --> DockerImage["Docker Image"];
    DockerImage -- "Pushes to" --> ContainerRegistry["Container Registry"];
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Build Process Description:

  1. Code Commit: Developers commit code changes to a Git repository (e.g., GitHub, GitLab).
  2. CI/CD Trigger: The code commit triggers a CI/CD pipeline (e.g., GitHub Actions, Jenkins).
  3. Testing: The pipeline runs automated tests (unit tests, integration tests) in a test environment.
  4. Static Analysis (SAST): A SAST scanner analyzes the source code for potential security vulnerabilities.
  5. Dependency Checking: A dependency checker scans the project's dependencies for known vulnerabilities.
  6. Build: If all tests and security checks pass, the pipeline builds a Docker image containing the application.
  7. Push to Registry: The Docker image is pushed to a container registry (e.g., Docker Hub, Azure Container Registry, Amazon ECR).

Security Controls in Build Process:

  • security control: Git Repository Access Control: Restrict access to the Git repository to authorized developers only.
  • security control: CI/CD Pipeline Security: Secure the CI/CD pipeline itself (e.g., using secrets management, access control).
  • security control: Automated Testing: Run comprehensive automated tests to catch bugs and potential security flaws early.
  • security control: Static Application Security Testing (SAST): Integrate SAST tools to identify vulnerabilities in the source code.
  • security control: Dependency Scanning: Use tools to scan project dependencies for known vulnerabilities.
  • security control: Container Image Scanning: Scan the built Docker image for vulnerabilities before pushing it to the registry.
  • security control: Build Artifact Signing: Digitally sign build artifacts to ensure their integrity.

RISK ASSESSMENT

Critical Business Processes:

  • The critical business processes depend on the specific application using MediatR. MediatR itself is a technical enabler, not a business process. Examples of business processes that might be supported by an application using MediatR:
    • User registration and authentication.
    • Order processing.
    • Financial transactions.
    • Data management and reporting.
    • Content delivery.

Data Sensitivity:

  • Again, this depends on the specific application. MediatR doesn't handle data directly, but the handlers within the application will. Examples of data that might be handled:
    • Personally Identifiable Information (PII): Names, addresses, email addresses, phone numbers (High Sensitivity).
    • Financial Data: Credit card numbers, bank account details (High Sensitivity).
    • Authentication Credentials: Usernames, passwords, API keys (High Sensitivity).
    • Business Data: Sales figures, customer data, internal documents (Variable Sensitivity - depends on the specific data).
    • Application Configuration Data: Database connection strings, API keys (High Sensitivity).
    • User Generated Content: Comments, posts, uploaded files (Variable Sensitivity).

QUESTIONS & ASSUMPTIONS

Questions:

  • What specific type of application will be using MediatR? (e.g., web application, API, background service)
  • What external systems will the application interact with? (e.g., databases, third-party APIs, message queues)
  • What are the specific security requirements of the application? (e.g., compliance regulations, data sensitivity)
  • What is the deployment environment for the application? (e.g., cloud, on-premise, containerized)
  • What is the existing CI/CD pipeline and build process?
  • What level of logging and monitoring is required?

Assumptions:

  • BUSINESS POSTURE: The organization values code quality, maintainability, and security.
  • SECURITY POSTURE: The organization has a basic understanding of secure software development practices. There are existing security controls for authentication.
  • DESIGN: The application will be designed using a modular approach, with clear separation of concerns. The application will likely interact with at least one external system (e.g., a database). The deployment will be containerized using Docker and Kubernetes. The build process will involve a CI/CD pipeline with automated testing and security checks.