Senior .NET Developer

We are seeking a Senior .NET Developer for a specialized project with the Dutch Tax Authority (Belastingdienst) focused on modernizing the authentication process within an employee support portal. The role involves analyzing, designing, supporting the implementation, and finalizing the transition from WS-Federation to a modern Identity Bridge solution. This position requires an average commitment of 2 days per week from May 1, 2026, to December 31, 2026. The successful candidate will conduct an IST analysis of the current WS-Federation application, map dependencies and technical impacts, and develop a SOLL design for the new authentication framework. You will also advise on the integration of a Reverse Proxy within the architecture and provide hands-on support during the implementation phase in the existing .NET environment. Additionally, you will identify and mitigate technical risks and collaborate with development teams, administrators, and stakeholders to ensure a smooth transition. A key aspect of this role is knowledge transfer to junior team members through coaching and guidance, ensuring continuity and further development within the team. The project is critical for maintaining an up-to-date, future-proof IT landscape within the IBS Toeslagen department, as the current WS-Federation setup does not align with future requirements and planned migrations.