Use sessionStorage instead of localStorage

[TomPichaud]

From #35

This would increase the security.

[ghost]

Thank you for adding this @TomPichaud, this PR needs to be added to the docs.

@sw-yx?

[swyxio]

not something i decide. tagging @bcomnes and @rybit

[erezrokah]

Closing as stale, not sure how this increases security and I think it is expected from auth libraries to maintain session between browser instances.
Regardless, that functionality can be implemented in user land.

Please comment if you have additional feedback