Chaïm Zonnenberg

Chaïm Zonnenberg

.NET Developer | Agentic Coding & Identity/SSO | 20+ years experience
De Bilt (Utrecht), Netherlands Born 1981 From September: room for 1-2 teams LinkedIn

Specialisations

I help teams change their way of working, from the inside, in the code.

Agentic coding for .NET teams

Daily practice on my own .NET SaaS since August 2025: building context, setting guardrails, setting up and refining agents. A workflow I want to bring to teams. Claude Code, GitHub Copilot.

Identity & SSO

OAuth2, OpenID Connect, SCIM, Azure Entra ID. Multiple secure token services built. IdentityServer4 to OpenIddict migrations. SC-300 certified.

I build daily with Claude Code on two products: Factuur-Assist.nl (135+ customers) and Invullen.nl. .NET 10, C#, Azure.

Personal Skills
Craftsmanship Change Management Hands-on Mentality Empathy Fast Learner Perseverance

What I've Done

  • Two own SaaS products built daily with AI tooling (Claude Code, GitHub Copilot)
  • Multiple secure token services built with IdentityServer4, OpenIddict and custom implementations
  • SCIM 2.0 provisioning endpoints for Azure Entra ID and Auth0, tested against enterprise tenant
  • IdentityServer4 migration to OpenIddict
  • AI chatbots and Semantic Kernel integrations in existing .NET applications
  • Own SaaS products in production on Azure: Invullen.nl and Factuur-Assist.nl
  • Microservices architecture advised and guided at financial institutions
Sectors
Financial Services Government & Law Enforcement Real Estate Education & Assessment

Freelance Experience

Period Client Role
Aug 2025 – present Software Assist (own practice) Agentic coding on own .NET SaaS (Invullen.nl, Factuur-Assist). Available for teams since Apr 2026.
Sep 2018 – present Software Assist (various clients) Identity & SSO Engineer - OAuth2, OpenID Connect, SCIM, .NET backend development
Aug 2016 – Jul 2018 ABN AMRO Mortgages Software Architect / Security Developer (Florius/Moneyou)
Nov 2014 – Aug 2016 PFZW/PGGM Pension Management Senior software developer
Oct 2013 – Sep 2014 Van Lanschot Bank BI / SQL Consultant
Jun 2013 – Sep 2013 Rubicon Database Developer
May 2012 – May 2013 ABN AMRO Mortgages Project Manager / Scrum Master
Oct 2011 – Apr 2012 Tensing Senior Developer .NET & SQL Server
Feb 2011 – Oct 2011 MyCom Software Developer

Employment

Period Employer Role
Mar 2009 – Jan 2011 Kadenza Lead Software Engineer / BI Consultant
Aug 2006 – Feb 2009 DTZ Zadelhoff Real Estate Data Manager
Aug 2005 – Aug 2006 DTZ Zadelhoff Software Developer

Ventures

Software Assist
2018 – present

Freelance consultancy. Senior .NET development, agentic coding and Identity/SSO solutions.

Invullen.nl
2025 – present

Survey platform. Built and launched independently.

Factuur Assist
2019 – present

Invoicing software. 135+ clients, built and managed independently.

Education

Degrees
MSc Computer Science

Utrecht University

2007
BSc Computer Science

Utrecht University

2006, cum laude
BSc Mathematics

Utrecht University

2006, cum laude
Certifications
Additional Training
  • Samensturingsacademie - Successful Entrepreneurship and Change 2023
  • Microsoft - Data Science 2017
  • DTZ Zadelhoff - Real Estate and Brokerage Traineeship 2006 – 2007

Tech Stack

AI
Claude Code Semantic Kernel OpenAI Azure AI Foundry
Identity
OAuth2 OpenID Connect Azure Entra ID SCIM IdentityServer4 OpenIddict
.NET & Cloud
.NET 10 C# Azure Docker Kubernetes (AKS) SQL Server
Frontend
Vue 2/3 Angular TypeScript
DevOps
Azure DevOps CI/CD Playwright

"Chaïm is a true professional. One you don't want to let go from day one. Proactive is his motto. He picks up what matters and doesn't let go until it's resolved."

Robert, IT Team Lead at financial institution

Specialist work that keeps getting postponed?

An hour-long call. Then you'll know if I'm the right person for your team.

Schedule an introduction