broken with upcoming oauth2 2.0 gem

[troex]

latest (master) version of oauth2 gem switched auth_scheme to basic_auth so it passes auth code in auth header instead see https://github.com/oauth-xx/oauth2/blob/4f57713f338bd8945ea7628a0f54660137c5c10c/CHANGELOG.md#unreleased

since omniauth-shopify-oauth2 depends on omniauth-oauth2 which depends on oauth2 - and all relay on "default" behaviour it is likely fail when oauth2 2.0 released.

Please set auth_scheme explicitly to request_body, this is easy to do with builder or inside the gem client_options:

use OmniAuth::Builder do
  provider :shopify, SHOPIFY_KEY, SHOPIFY_SECRET,
    client_options: {
      auth_scheme: :request_body
    }
end