Good morning!
If I understand the problem correctly, all you're looking for is the username from their login on the computer, not the full username and password, correct?
If that is the case, I dug up a support article covering the retrieval of a Windows Username using the Systems Exec VI or through a Property Node.
Retrieve Windows User Name in LabVIEW Programmatically:
Link: https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000PACwSAO
Tyler O.
Applications Engineer
National Instruments