[app-server] read rate limits API (#5302)

Adds a `GET account/rateLimits/read` API to app-server. This calls the
codex backend to fetch the user's current rate limits.

This would be helpful in checking rate limits without having to send a
message.

For calling the codex backend usage API, I generated the types and
manually copied the relevant ones into `codex-backend-openapi-types`.
It'll be nice to extend our internal openapi generator to support Rust
so we don't have to run these manual steps.

# External (non-OpenAI) Pull Request Requirements

Before opening this Pull Request, please read the dedicated
"Contributing" markdown file or your PR may be closed:
https://github.com/openai/codex/blob/main/docs/contributing.md

If your PR conforms to our contribution guidelines, replace this text
with a detailed and high quality description of your changes.

codex-rs/app-server/tests/common/Cargo.toml

@@ -9,7 +9,10 @@ path = "lib.rs"
 [dependencies]
 anyhow = { workspace = true }
 assert_cmd = { workspace = true }
+base64 = { workspace = true }
+chrono = { workspace = true }
 codex-app-server-protocol = { workspace = true }
+codex-core = { workspace = true }
 serde = { workspace = true }
 serde_json = { workspace = true }
 tokio = { workspace = true, features = [

codex-rs/app-server/tests/common/auth_fixtures.rs

@@ -0,0 +1,131 @@
+use std::path::Path;
+
+use anyhow::Context;
+use anyhow::Result;
+use base64::Engine;
+use base64::engine::general_purpose::URL_SAFE_NO_PAD;
+use chrono::DateTime;
+use chrono::Utc;
+use codex_core::auth::AuthDotJson;
+use codex_core::auth::get_auth_file;
+use codex_core::auth::write_auth_json;
+use codex_core::token_data::TokenData;
+use codex_core::token_data::parse_id_token;
+use serde_json::json;
+
+/// Builder for writing a fake ChatGPT auth.json in tests.
+#[derive(Debug, Clone)]
+pub struct ChatGptAuthFixture {
+    access_token: String,
+    refresh_token: String,
+    account_id: Option<String>,
+    claims: ChatGptIdTokenClaims,
+    last_refresh: Option<Option<DateTime<Utc>>>,
+}
+
+impl ChatGptAuthFixture {
+    pub fn new(access_token: impl Into<String>) -> Self {
+        Self {
+            access_token: access_token.into(),
+            refresh_token: "refresh-token".to_string(),
+            account_id: None,
+            claims: ChatGptIdTokenClaims::default(),
+            last_refresh: None,
+        }
+    }
+
+    pub fn refresh_token(mut self, refresh_token: impl Into<String>) -> Self {
+        self.refresh_token = refresh_token.into();
+        self
+    }
+
+    pub fn account_id(mut self, account_id: impl Into<String>) -> Self {
+        self.account_id = Some(account_id.into());
+        self
+    }
+
+    pub fn plan_type(mut self, plan_type: impl Into<String>) -> Self {
+        self.claims.plan_type = Some(plan_type.into());
+        self
+    }
+
+    pub fn email(mut self, email: impl Into<String>) -> Self {
+        self.claims.email = Some(email.into());
+        self
+    }
+
+    pub fn last_refresh(mut self, last_refresh: Option<DateTime<Utc>>) -> Self {
+        self.last_refresh = Some(last_refresh);
+        self
+    }
+
+    pub fn claims(mut self, claims: ChatGptIdTokenClaims) -> Self {
+        self.claims = claims;
+        self
+    }
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct ChatGptIdTokenClaims {
+    pub email: Option<String>,
+    pub plan_type: Option<String>,
+}
+
+impl ChatGptIdTokenClaims {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn email(mut self, email: impl Into<String>) -> Self {
+        self.email = Some(email.into());
+        self
+    }
+
+    pub fn plan_type(mut self, plan_type: impl Into<String>) -> Self {
+        self.plan_type = Some(plan_type.into());
+        self
+    }
+}
+
+pub fn encode_id_token(claims: &ChatGptIdTokenClaims) -> Result<String> {
+    let header = json!({ "alg": "none", "typ": "JWT" });
+    let mut payload = serde_json::Map::new();
+    if let Some(email) = &claims.email {
+        payload.insert("email".to_string(), json!(email));
+    }
+    if let Some(plan_type) = &claims.plan_type {
+        payload.insert(
+            "https://api.openai.com/auth".to_string(),
+            json!({ "chatgpt_plan_type": plan_type }),
+        );
+    }
+    let payload = serde_json::Value::Object(payload);
+
+    let header_b64 =
+        URL_SAFE_NO_PAD.encode(serde_json::to_vec(&header).context("serialize jwt header")?);
+    let payload_b64 =
+        URL_SAFE_NO_PAD.encode(serde_json::to_vec(&payload).context("serialize jwt payload")?);
+    let signature_b64 = URL_SAFE_NO_PAD.encode(b"signature");
+    Ok(format!("{header_b64}.{payload_b64}.{signature_b64}"))
+}
+
+pub fn write_chatgpt_auth(codex_home: &Path, fixture: ChatGptAuthFixture) -> Result<()> {
+    let id_token_raw = encode_id_token(&fixture.claims)?;
+    let id_token = parse_id_token(&id_token_raw).context("parse id token")?;
+    let tokens = TokenData {
+        id_token,
+        access_token: fixture.access_token,
+        refresh_token: fixture.refresh_token,
+        account_id: fixture.account_id,
+    };
+
+    let last_refresh = fixture.last_refresh.unwrap_or_else(|| Some(Utc::now()));
+
+    let auth = AuthDotJson {
+        openai_api_key: None,
+        tokens: Some(tokens),
+        last_refresh,
+    };
+
+    write_auth_json(&get_auth_file(codex_home), &auth).context("write auth.json")
+}

codex-rs/app-server/tests/common/lib.rs

@@ -1,7 +1,12 @@
+mod auth_fixtures;
 mod mcp_process;
 mod mock_model_server;
 mod responses;
 
+pub use auth_fixtures::ChatGptAuthFixture;
+pub use auth_fixtures::ChatGptIdTokenClaims;
+pub use auth_fixtures::encode_id_token;
+pub use auth_fixtures::write_chatgpt_auth;
 use codex_app_server_protocol::JSONRPCResponse;
 pub use mcp_process::McpProcess;
 pub use mock_model_server::create_mock_chat_completions_server;

codex-rs/app-server/tests/common/mcp_process.rs

@@ -236,6 +236,11 @@ impl McpProcess {
         self.send_request("getUserAgent", None).await
     }
 
+    /// Send an `account/rateLimits/read` JSON-RPC request.
+    pub async fn send_get_account_rate_limits_request(&mut self) -> anyhow::Result<i64> {
+        self.send_request("account/rateLimits/read", None).await
+    }
+
     /// Send a `userInfo` JSON-RPC request.
     pub async fn send_user_info_request(&mut self) -> anyhow::Result<i64> {
         self.send_request("userInfo", None).await