Non-Google Account Using chrome.identity - rest

Question

I'm trying to make a Gogle Chrome extension that requires user authorization to a SugarCRM 7.5 instance with OAuth 2.0 and I need to store the access token that's retrieved. I may need more clarification on how launchWebAuthFlow works.
Firstly, I can retrieve an access token from SugarCRM by using a POST request (not a GET request) that returns an access and a refresh token.
When I tried using the code below I kept getting the error: "authorization url can not be loaded" and when I checked the background console (I already know that my auth URL is wrong). Any help is appreciated even if you don't know SugarCRM. Just a general answer that can get me started is much appreciated.
manifest.json
{
"name": "Auth Sample",
"version": "1",
"manifest_version": 2,
"minimum_chrome_version": "29",
"key": "<long key>",
"app": {
"background": {
"scripts": ["background.js"]
}
},
"permissions": [
"identity",
"https://<sugar instance>/*"
]
}
Background.js
chrome.identity.launchWebAuthFlow(
{'url': '<url-to-do-auth>', 'interactive': true},
function(redirect_url) { console.log(redirect_url); });
My URL is definitely not gonna work here but it's something like this:
var client_id = '<client id from Oauth 2.0>';
var redirectUri = chrome.identity.getRedirectURL("sugarcrm");
var url = "https://<sugar instance base url>/rest/v10/oauth2/token?client_id=" + client_id + "&callbackURL=" + redirectUri + "&response_type=token"
What's the url-to-do-auth (is this the URL to do a regular login (username and password) to SugarCRM or is it a GET request through the REST API to do login)
I don't have a UI web auth flow for my SugarCRM instance. Is it possible to create one from the application or should that be on the server?
I can only make POST requests to get an access token. Will that still work with launchWebAuthFlow?
Update
I ended up storing the token using the local chrome.storage api and only stored the refresh token which will keep getting a new access token every time the application is run(I think it's more secure than just storing the access token as that will force it to always keep changing without passing other credentials)
After more search on launchWebAuthFlow. I found out that the url launchWebAuthFlow takes as parameter will launch a web page(with interactive parameter set to true) which is hosted on the server, that will let the user login and will return an access token if success. This url is actually an endpoint on the restful server. You need to create this endpoint that will be a get request with some parameters including a callbackURL, client_id and response_type. Then it will respond with another function that will be a post request and will take the username and password. If credentials are correct, it will return the access token as a parameter in the callbackURL(chrome extension specific url that contains the extension ID).
Please feel free to correct me or add something if I'm wrong.