Updated registration endpoint for dbAuth to accomodate other posted registration data. 
Also added some new dbAuth properties
1. usernameMinLength : specify minimum length of username (5)
2. usernameMaxLength : specify maximum length of username (40)
3. usernamePattern : specify regex pattern for usernames ('/^[A-Za-z0-9]+$/') // defaults to alphanumeric chars only

Formatted section on setting up JWT authentication to make the list more readable

Registration w/ addl data

Added the dbAuth properties for checking minimum and maximum length of username as well as allowed characters.

Since we're processing additional data during registration, we need to check if these data were defined in db to be unique. 
For example, email addresses are usually used just once in an application. We can query the database to check if the new email address is not yet registered, but, in some cases, we may more than 2 or 3 or more unique fields (not common, but possible), hence we would also need to query 2,3 or more times. 

As a TEMPORARY WORKAROUND, we'll just attempt to register the new user and wait for the db to throw a DUPLICATE KEY EXCEPTION.

Changes
$_SESSION['user']['updatedAt'] - set to time when the session was created/updated
dbAuth.refreshSession - number of minutes after which the session data is refreshed when the /me end-point is called

Option to update session data via /me end-point

Changes
$usernamePattern - defaults  to  /^\p{L}+$/u , visible characters, no punctuation or numbers, unicode mode
$usernameMaxLength - defaults to 255
changed validation of other inputs from filter_validate()  to htmlspecialchars()
fixed typos missing and extra $