feat: parse info from auth.json and show in /status (#1923)

- `/status` renders
    ```
    signed in with chatgpt
      login: example@example.com
      plan: plus
    ```
- Setup for using this info in a few more places.

---------

Co-authored-by: Michael Bolin <mbolin@openai.com>

codex-rs/login/src/token_data.rs

@@ -0,0 +1,117 @@
+use base64::Engine;
+use serde::Deserialize;
+use serde::Serialize;
+use thiserror::Error;
+
+#[derive(Deserialize, Serialize, Clone, Debug, PartialEq, Default)]
+pub struct TokenData {
+    /// Flat info parsed from the JWT in auth.json.
+    #[serde(deserialize_with = "deserialize_id_token")]
+    pub id_token: IdTokenInfo,
+
+    /// This is a JWT.
+    pub access_token: String,
+
+    pub refresh_token: String,
+
+    pub account_id: Option<String>,
+}
+
+/// Flat subset of useful claims in id_token from auth.json.
+#[derive(Debug, Clone, PartialEq, Eq, Default, Serialize)]
+pub struct IdTokenInfo {
+    pub email: Option<String>,
+    /// The ChatGPT subscription plan type
+    /// (e.g., "free", "plus", "pro", "business", "enterprise", "edu").
+    /// (Note: ae has not verified that those are the exact values.)
+    pub chatgpt_plan_type: Option<String>,
+}
+
+#[derive(Deserialize)]
+struct IdClaims {
+    #[serde(default)]
+    email: Option<String>,
+    #[serde(rename = "https://api.openai.com/auth", default)]
+    auth: Option<AuthClaims>,
+}
+
+#[derive(Deserialize)]
+struct AuthClaims {
+    #[serde(default)]
+    chatgpt_plan_type: Option<String>,
+}
+
+#[derive(Debug, Error)]
+pub enum IdTokenInfoError {
+    #[error("invalid ID token format")]
+    InvalidFormat,
+    #[error(transparent)]
+    Base64(#[from] base64::DecodeError),
+    #[error(transparent)]
+    Json(#[from] serde_json::Error),
+}
+
+pub(crate) fn parse_id_token(id_token: &str) -> Result<IdTokenInfo, IdTokenInfoError> {
+    // JWT format: header.payload.signature
+    let mut parts = id_token.split('.');
+    let (_header_b64, payload_b64, _sig_b64) = match (parts.next(), parts.next(), parts.next()) {
+        (Some(h), Some(p), Some(s)) if !h.is_empty() && !p.is_empty() && !s.is_empty() => (h, p, s),
+        _ => return Err(IdTokenInfoError::InvalidFormat),
+    };
+
+    let payload_bytes = base64::engine::general_purpose::URL_SAFE_NO_PAD.decode(payload_b64)?;
+    let claims: IdClaims = serde_json::from_slice(&payload_bytes)?;
+
+    Ok(IdTokenInfo {
+        email: claims.email,
+        chatgpt_plan_type: claims.auth.and_then(|a| a.chatgpt_plan_type),
+    })
+}
+
+fn deserialize_id_token<'de, D>(deserializer: D) -> Result<IdTokenInfo, D::Error>
+where
+    D: serde::Deserializer<'de>,
+{
+    let s = String::deserialize(deserializer)?;
+    parse_id_token(&s).map_err(serde::de::Error::custom)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde::Serialize;
+
+    #[test]
+    #[expect(clippy::expect_used, clippy::unwrap_used)]
+    fn id_token_info_parses_email_and_plan() {
+        // Build a fake JWT with a URL-safe base64 payload containing email and plan.
+        #[derive(Serialize)]
+        struct Header {
+            alg: &'static str,
+            typ: &'static str,
+        }
+        let header = Header {
+            alg: "none",
+            typ: "JWT",
+        };
+        let payload = serde_json::json!({
+            "email": "user@example.com",
+            "https://api.openai.com/auth": {
+                "chatgpt_plan_type": "pro"
+            }
+        });
+
+        fn b64url_no_pad(bytes: &[u8]) -> String {
+            base64::engine::general_purpose::URL_SAFE_NO_PAD.encode(bytes)
+        }
+
+        let header_b64 = b64url_no_pad(&serde_json::to_vec(&header).unwrap());
+        let payload_b64 = b64url_no_pad(&serde_json::to_vec(&payload).unwrap());
+        let signature_b64 = b64url_no_pad(b"sig");
+        let fake_jwt = format!("{header_b64}.{payload_b64}.{signature_b64}");
+
+        let info = parse_id_token(&fake_jwt).expect("should parse");
+        assert_eq!(info.email.as_deref(), Some("user@example.com"));
+        assert_eq!(info.chatgpt_plan_type.as_deref(), Some("pro"));
+    }
+}