National digital identity systems have become a key requirement for easy access to online public services, specially during Covid-19. While many countries have adopted a national digital identity system, many are still in the process of establishing one. Through a comparative analysis of the technological and legal dimensions of a few selected national digital identity solutions currently being used in different countries, we highlight the diversity of technologies and architectures and the key role of the legal framework of a given digital identity solution. We also present several key issues related to the implementation of these solutions, how to ensure the State sovereignty over them, and how to strike the right balance between private sector and public sector needs. This position paper aims to help policy makers, software developers and concerned users understand the challenges of designing, implementing and using a national digital identity management system and establishing a legal framework for digital identity management, including personal data protection measures. The authors of this paper have a favorable position for self-sovereign identity management systems that are based on Blockchain technology, and we believe they are the most suitable for national digital identity systems.