Handle edge case in user authentication

[birtony]

When the user signs in the first time, we save accessToken and subjectId to localStorage. Then, on subsequent sing in attempts, we fetch those parameters and use them to initialize agent instance. However, if the user manually goes into browser settings and clears the subjectId, we won't have anywhere to get it from to initialize the agent instance. We need to add logic to fetch subjectId from the requestAccess response in this case (auth server returns both accessToken and subjectId in case user's keypair has already been used to register the user)