Add support for a separate chatgpt auth endpoint (#1712)

Adds a `CodexAuth` type that encapsulates information about available
auth modes and logic for refreshing the token.
Changes `Responses` API to send requests to different endpoints based on
the auth type.
Updates login_with_chatgpt to support API-less mode and skip the key
exchange.

codex-rs/chatgpt/src/chatgpt_token.rs

@@ -18,7 +18,10 @@ pub fn set_chatgpt_token_data(value: TokenData) {
 
 /// Initialize the ChatGPT token from auth.json file
 pub async fn init_chatgpt_token_from_auth(codex_home: &Path) -> std::io::Result<()> {
-    let auth_json = codex_login::try_read_auth_json(codex_home).await?;
-    set_chatgpt_token_data(auth_json.tokens.clone());
+    let auth = codex_login::load_auth(codex_home)?;
+    if let Some(auth) = auth {
+        let token_data = auth.get_token_data().await?;
+        set_chatgpt_token_data(token_data);
+    }
     Ok(())
 }