Omniauth.params are empty hash (api_only) - ruby-on-rails

Question

Environment
Ruby 2.7.4 (Rails API only)
Rails 6.0.4.1
Devise 4.8.0
Omniauth1.8.1
Current behavior
Getting omniauth missing_credentials? error. The request.params is always an empty hash even though I provide username and password in the request body via POST method. I can see the body params when debugging actual controller, but it looks like those params are not passed to omniauth request.
Controller:
module Api
module V1
module Auth
class OmniauthCallbacksController < Devise::OmniauthCallbacksController #< ApplicationController#
include ActionController::Cookies
def ldap
puts request.env['omniauth.auth'] # => NULL
end
def failure
puts "request.env['omniauth.auth']: #{request.env['omniauth.auth']}" # => NULL
puts "request.env['omniauth.params']: #{request.env['omniauth.params']}" # => {}
puts "params: #{params}" # => { "username": "myusername", "password": "mypassword" }
render json: { status: "fail" }
end
end
end
end
end
Application.rb:
config.api_only = true
config.session_store :cookie_store, key: '_interslice_session'
config.middleware.use ActionDispatch::Cookies
config.middleware.use config.session_store, config.session_options
Routes.rb:
devise_for :users, controllers: { omniauth_callbacks: 'api/v1/auth/omniauth_callbacks' }
Devise.rb:
config.omniauth :ldap, :host => 'XXX.com',
:port => 389,
:method => :plain,
:base => 'cn=accounts,dc=int,dc=dostack,dc=io',
:uid => 'uid',
:try_sasl => false,
:bind_dn => "uid=XXX,cn=users,cn=accounts,dc=int,dc=dostack,dc=io",
:password => "xxxxxxxx"
Response:
Expected behavior
Authenticate using omniauth (LDAP or using any other omniauth provider)