dbAuth Vercel Fix

[cannikin]

Fixes two issues that Vercel was blowing up on:

1. Vercel does not like having a return body that's JSON and turning it into a string for us—it MUST be a string
2. If the body is empty, Vercel will still set isBase64Encoded to true, and you can't decode an empty string

Fixing these introduced another issue, where getToken returned an empty string which a client call for getUserMetadata interpreted as there being a user logged in and so would call the GraphQL endpoint for getCurrentUser, which then returned a 500. This is patched as well.

(Potential) Breaking Change

Serverless functions may already wait for async code to complete before returning (this hasn't been an issue in dev or a serverfull deployment). But in case they don't, anyone already using dbAuth should update their api/src/functions/auth.js to include an await on the final line of code:

Before:

return authHandler.invoke()

After:

return await authHandler.invoke()

[cannikin]

Verified that deploy works to Netlify as well: https://jolly-bohr-d8f980.netlify.app/

[dac09]

LGTM! Thanks Lord Cannakin!

[cannikin]

That's Cann i kin! 😃