Authentication

noun

1. The act of authenticating, verifying, or establishing the authoritativeness, genuineness, validity, credibility, or truth of anything; specifically, in law, the official attestation of a written instrument.
2. a mark on an article of trade to indicate its origin and authenticity.
3. validating the authenticity of something or someone.
4. something which validates or confirms the authenticity of something
5. proof of the identity of a user logging on to some network