Can't use sequelize commands, despite many iterations of perms and users

Linux Pop! distribution (v 17 Ubuntu) Custom-built desktop machine

I've been working for a long time to try to get just a simple sequelize db:migrate command to work.

I have postgresql installed and if I do su - postgres and then psql I can get into the psql commannd prompt (and can also get out, using \q).

I'm working on a project where we need to use the sequelize-cli manager. I've installed npm i --save [email protected] [email protected] [email protected].

Then I did sequelize init in my directory, and adjusted the database files.

const path = require("path");

module.exports = {
  "config": path.resolve("./db/config", "config.json"),
  "models-path": path.resolve("./db/models"),
  "seeders-path": path.resolve("./db/seeds"),
  "migrations-path": path.resolve("./db/migrations")
};

And here's my config.json file for sequelize:

{
  "development": {
    "username": "postgres",
    "password": null,
    "database": "address-bloc-dev",
    "host": "127.0.0.1",
    "dialect": "postgres",
    "logging": false
  },
  "test": {
    "username": "postgres",
    "password": null,
    "database": "address-bloc-test",
    "host": "127.0.0.1",
    "dialect": "postgres",
    "logging": false
  }
}

No matter what I do, whenever I try to do sequelize db:migrate, I get this:

$ sequelize db:migrate

Sequelize CLI [Node: 6.11.4, CLI: 4.0.0, ORM: 4.32.6]

Loaded configuration file "db/config/config.json".
Using environment "development".
sequelize deprecated String based operators are now deprecated. Please use Symbol based operators for better security, read more at http://docs.sequelizejs.com/manual/tutorial/querying.html#operators node_modules/sequelize/lib/sequelize.js:237:13

ERROR: password authentication failed for user "postgres"

I get this error whether I'm logged in as my main, normal user, or when I'm logged in as postgres. I can su between the two, navigate to the correct directory, and still get the same result.

I was earlier also getting another error, postgres is not in the sudoers file. This incident will be reported..

Per a recommendation on stackoverflow, I tried adding the postgres user to sudo usermod -a -G sudo postgres and made postgres an official account. It shows up on my login screen.

This did manage to make that second sudoers... error go away.

However, I still ultimately get the same password authentication failure... error.

I've also tried installing npm both as a regular user, and with the sudo command.

And I've tried going into the pg_hba.config file and changing peer to ident, per another recommendation on stackoverflow. No luck, still.

Any ideas about why I can't get sequelize-cli to perform this operation?

EDIT: I've received some kind responses, but so far I haven't been able to figure out what I'm doing wrong. Made some notes in a comment. Thank you.