There were rumors about OpenAI preparing for sign in with OpenAI to let users use their OpenAI allowances with apps, si this is basically it. The question is, how long before OpenAI bans this or makes it official.
This is a way to let users use the Codex-app to Codex-model interface that the 20$ subscription uses so that other apps can use the OpenAI API without paying per token.
What you are describing is SSO with OpenAI as an identity provider