eIDAS stands for "electronic IDentification, Authentication and trust Services," and is the commonly used name for the EU regulation 910/2014 governing electronic identification and trust services for European Union Member States. The regulation aims to promote cross-border cooperation and the interoperability of national digital identity (eID) systems to make it more convenient for citizens and businesses to access online public services in the various member states that offer access via eID authentication.

By clicking on the "Login with eIDAS" button, a page is shown asking me to choose one of the nationalities listed. If my nationality is present, by selecting it I can complete the authentication process and access the requested service.

An EU citizen, requests to log in to an Italian public online service using the digital identity. To verify their identity, the service of the public administration communicates with the national eIDAS node. The Italian eIDAS node transmits the request to the eIDAS node of the user's country. The identity is verified by the identity and attribute provider in the user's country. The verified identity is sent to the Italian administration that owns the service, which allows the user to access the online service

The "Login with eIDAS button" is present on the websites of PA service providers that provide services that can be used by foreign citizens with an eID (Digital Identity) recognized in the eIDAS area