'auth' originates from English, specifically the word 'authentication' (a clipped form), where the element 'auth-' comes from Greek 'authentikos' meaning 'real, genuine'.

'auth' changed from the full English word 'authentication' (and related 'authorize') as an informal clipping used in computing and tech jargon, eventually becoming the common shorthand 'auth' in modern technical contexts.

Initially, the root referred to being 'genuine' or 'authoritative' (from Greek), then to processes named 'authentication'/'authorization'; over time the clipped form 'auth' came to mean either the process of verifying identity or the permission/credentials themselves in tech usage.