Implement Billing API with Authentication, Invoices, and API Documentation

[sweep-ai]

This pull request was created by Sweep to resolve the following request by @curtisdelicata:

Description: Provide a public API for external integrations (e.g., CRM, accounting software).

Tasks:
Design and implement RESTful API endpoints.
Develop API documentation.
Implement authentication and rate limiting.
Acceptance Criteria:
External systems can access billing data via the API.
API access is secure and well-documented.

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Purpose

Enhance the billing system by introducing a comprehensive API infrastructure with robust authentication, invoice management, and standardized API documentation.

Description

This pull request establishes a complete API ecosystem for the billing application, focusing on the following key areas:

1. Authentication Mechanism

• Implemented secure token-based authentication using Laravel Sanctum
• Added /auth/token endpoint for generating API tokens
• Included token revocation methods for enhanced security

2. Invoice Management

• Created a full-featured InvoiceController with CRUD operations
• Implemented filtering and pagination for invoice retrieval
• Added invoice download functionality via PDF generation
• Developed comprehensive validation for invoice creation and updates

3. API Documentation

• Generated OpenAPI (Swagger) specification in docs/api.yaml
• Defined comprehensive API endpoint schemas and request/response structures
• Included security definitions for bearer token authentication

4. API Route Configuration

• Restructured routes/api.php with clear route grouping
• Added protected routes with authentication and rate limiting
• Organized routes for invoices, subscriptions, and customers

Summary

• Added AuthController for token-based authentication
• Implemented InvoiceController with full CRUD functionality
• Created InvoiceResource for standardized API responses
• Generated OpenAPI specification in docs/api.yaml
• Updated routes/api.php with new protected routes
• Introduced rate limiting and authentication middleware