Ömürcan Özcan
Selected work

SYSTEM 02 / LEGACY SYSTEMS · BACKEND ARCHITECTURE

Legacy-to-API Modernization

The most important thing in an existing system is often the behavior people already depend on.

My scope
PHP modernization · Node.js/MSSQL APIs · Authentication · Data models
  • PHP
  • Node.js
  • SQL Server
  • Sequelize
  • REST APIs
  • JWT
  • RBAC

Conceptual architecture

Where do identity, permissions and data meet?

  1. Authentication
  2. Permissions & validation
  3. SQL Server data

JWT identifies the caller. Permission checks and input validation sit at the Node.js API boundary; Sequelize models connect that boundary to MSSQL data.

PHPExisting workflowsBehavior · Rules · Data
Preserve the contractAccess · Validation
APIModular servicesNode.js · SQL Server

OPERATIONAL CONTEXT

Understand the existing system.

At the Istanbul Chamber of Pharmacists, legacy PHP workflows support member services, payments, scheduling and internal operations. My modernization work moves these workflows into Node.js/MSSQL APIs.

MY RESPONSIBILITY

My contribution and scope

I implemented JWT authentication, permission-based access control, Sequelize data models, validation, integrations and operational reporting as part of this modernization work.

DECISIONS & RATIONALE

A cleaner boundary around existing behavior.

01

Modular APIs for legacy workflows

API modules give existing PHP workflows a defined backend boundary in Node.js, with MSSQL supplying the relational data.

02

Make access explicit

JWT handles authentication, while permission-based access control governs allowed actions. Input validation sits alongside both, keeping identity, authorization and request checks explicit in the API.

03

Keep data connected

Sequelize models connect the APIs to MSSQL. Integrations and reporting cover how those records are exchanged and used by the organization.

Let’s talk about your system.

Modernizing a workflow people already depend on? Let’s discuss its rules, data and integrations.