Authentication using Resource Owner Password Credentials in Rails - ruby-on-rails

Question

I am considerably new to OAuth authentication scheme. What pose a problem for me at the moment is getting access_token from server in Rails app.
So far I read few articles covering methods related to Resource Owner Password Credentials in OAuth 2.0, but still it got me nowhere.
To name a few Official documentation regarding ROPC / Introduction to OAuth2 / Description of OAuth2 gem from Intridea
Server that I want to connect with allows password grant. It's deployed by 3rd party, so I assume everything is ok with it. On manual page they defined example of authorization as follows:
curl -X POST -d
'grant_type=password&username=USER_EMAIL&password=YOUR_PASSWORD&client_id=CLIENT_ID&client_secret=CLIENT_SECRET'
'https://auth.example.com/oauth2/token'
I posses all data which is mentioned above. BTW, client_id and client_secret are generic values enclosed in documentation. Server uses Doorkeeper gem to implement OAuth2.
To retrieve access_token from server, I simply put advised by Doorkeeper's wiki code into one of my controllers. Testing ROPC for Doorkeeper
My code in Rails API app utilizing OAuth2 gem from Intridea:
def test
client = OAuth2::Client.new(CLIENT_ID, CLIENT_SECRET,
site: 'https://auth.example.com/oauth2/token')
access_token = client.password.get_token(username, password)
Rails.logger.info access_token.token
end
What I get after visiting localhost/test is Completed 500 Internal Server Error with OAuth2::Error saying that page that I look for doesn't exist.
When trying just use curl from command line with respective data, I recieve:
WWW-Authenticate: Bearer realm="Doorkeeper", error="invalid_grant", error_description="The provided authorization grant is invalid, expired, revoked, does not match the redirection URI used in the authorization request, or was issued to another client."
Please kindly advise what may cause problem in these set-up.

Answer 1

As it seems I overlooked one important thing, we should declare explicitly token_url in relation to site address and not treat site parameter as entire path.
So in order to request access_token my method should look like this:
def test
client = OAuth2::Client.new(client_id,
client_secret,
token_url: "/oauth2/token",
site: "https://www.example.com/" )
access_token = client.password.get_token(username, password)
Rails.logger.info access_token.token
end
Here you can find similar issue to mine.
If someone wants to get access token with password credentials using simple http method, here is example how to approach this thing:
def test
param = {
:client_id => client_id,
:client_secret => client_secret,
:grant_type => 'password',
:username => username,
:password => password
}
uri = URI.parse(service_url)
http = Net::HTTP.new(uri.host, uri.port)
http.verify_mode = OpenSSL::SSL::VERIFY_NONE
http.use_ssl = true
request = Net::HTTP::Post.new(uri.request_uri)
request.body = param.to_query
response = http.request(request)
Rails.logger.info response.body()
end