how_to_change_token_endpoint_auth_method.rb

require 'jwt'
require 'omniauth/strategies/oauth2'
require 'uri'

# {"error":"invalid_client",
#  "error_description":"Client authentication failed(e.g., unknown client, no client auth entication included, or unsupported authentication method)",
#  "error_hint":"The OAuth 2.0 Client supports client authentication method \"client_secret_basic\", but method \"client_secret_post\" was requested. You must configure the OAuth 2.0 client's \"token_endpoint_auth_method\" value to accept \"client_secret_post\".",
#  "status_code":401}

# How to change token_endpoint_auth_method value to "client_secret_basic"?
# Please change "auth_scheme" value to ":basic_auth".(Default is :request_body)

module OmniAuth
  module Strategies
    class MyClient < OmniAuth::Strategies::OAuth2
      ALLOWED_ISSUERS = ['https://localhost:3000/'].freeze
      BASE_SCOPE_URL = 'https://localhost:3000/oauth2/auth'
      BASE_SCOPES = %w[profile email openid].freeze
      DEFAULT_SCOPE = 'email,profile'
      USER_INFO_URL = 'https://localhost:3000/userinfo'

      option :name, 'myclient'
      option :authorize_options, %i[access_type hd login_hint prompt request_visible_actions scope state redirect_uri include_granted_scopes openid_realm device_id device_name]
      option :authorized_client_ids, []

      option :client_options,
             auth_scheme: :basic_auth,  # !!! Default is :request_body !!!
             site: 'https://localhost:3000',
             authorize_url: 'https://localhost:3000/oauth2/auth',
             token_url: 'https://localhost:3000/oauth2/token'