What is most likely the cause of a developer not being prompted for credentials when accessing an older file server from Windows Server 2019?

When a developer accesses an older file server from Windows Server 2019 without being prompted for credentials, it is likely due to the file server using SMB 1 (Server Message Block version 1), a protocol that is not enabled by default in Windows Server 2019.

Windows Server 2019 has SMB 1 disabled because it is considered obsolete and has known security vulnerabilities. If the file server is operating with SMB 1, the server may allow access without requiring authentication, particularly if the file share permissions grant access to the user or system context that is being used. This could lead to the developer being able to access files without being prompted for credentials, as the client may silently fall back to the SMB 1 protocol.

The reliance on outdated protocols, such as SMB 1, is a common consideration when interfacing with legacy systems. In modern environments, it's generally advisable to ensure that all systems are upgraded to use more secure protocols like SMB 2 or SMB 3 to enhance security while accessing file shares.