feat(auth): authenticate user with existing v1 credentials

closes #114

Changes

allow user to be logged in if user has credentials from v1

Implementation

check if user exist in db
if user exist, check if user is using old credentials
if user has v1 credentials, run authenticate fn (compareSync(...)).
... back to nextauth authentication flow ...

Notes

some users have emails that are not in the supported email domain list. we will intentionally force password reset with an email that's supported to remove such outliers (~2%) of users

Testing

Local only

run prisma migrate reset to reset your local db
run the app and head to the login page
login with this user + password, generated from the script below (see #sanity-check)
```
user: test_hash_pwd@smu.edu.sg
pwd: P@ssw0rd
```
login successfully

Sanity Check

to confirm the validity of my implemenation, you can try:

const bcrypt = require("bcrypt");

const saltRounds = 10;  // irrelevant for us
const pwd = "ExampleUnsafePassword!!!";  
const hash = bcrypt.hashSync(pwd, saltRounds);

console.log(hash);
// something that looks like `$2b$10$PkCVxT6KrNlBnXQJvwg.8eviXHaOpTOB5hO8P0K0m/15rGORToOXi`

console.log(bcrypt.compareSync(pwd, hash));  // true

or you can ask for your currently live afterclass.io user's password digest and i can send it to you securely for your own sanity check

AfterClass-io / afterclass.io-v2

feat(auth): authenticate user with existing v1 credentials #128