Ever since Google has launched a new version of the Gmail, back in 2007, some people wondered why Gmail's address includes a parameter called "shva"
"Just curious, what does the SHVA parameter in the new gmail URL stand for? Is it an acronym? I'm not really asking about the technical usage or the functionality; I'm just interested in the choice of the name," and asked BRKR. "I know GMail is not an Open-Source program so we can trace the code. But every website tries to make the URL shorter so that they ideally shouldn't add redundant data to the URL," thinks Omar Dolaimy.
According to the Mike Sego a former Gmail engineer, "shva" is an acronym for "should have a valid authentication". Apparently, the parameter is only included with after a successful authentication.