people are who they claim to be

(authentication: The process for verifying that people are who they claim to be.
For example, confirming the source and integrity of a sender’s digital signature by verifying it with the issuing certificate authority (CA).)

Could you please help me with the meaning of the bold clause in the above sentence.

It is a way of showing that the person who says he is Galilom2002 really is Galilom2002, and not an imposter.