Enforce managed authentication requirements locally (#37132)

## Why

Authentication restrictions must apply before stored or environment-provided credentials can be used, including during bootstrap before cloud requirements are fetched.

## What changed

- Add local `requirements.toml` allowlists for login methods and ChatGPT workspaces. Ignore these fields in cloud-provided requirements.
- Combine managed workspace allowlists with existing workspace restrictions by intersection, and fail closed when the resulting policy permits no usable login method.
- Centralize policy checks in the authentication manager so CLI, TUI, app-server, external-auth, and credential-loading paths consistently reject disallowed authentication before token hydration or network requests.

## Testing

- Cover policy composition, workspace intersection, invalid stored and external credentials, bootstrap enforcement, and login endpoint restrictions.

GitOrigin-RevId: efef22b248f3c3333e9aa55423e539efa2d2dd48

codex-rs/cli/src/main.rs

@@ -1821,16 +1821,19 @@ async fn load_exec_server_remote_auth_provider(
     use_agent_identity_auth: bool,
 ) -> anyhow::Result<codex_api::SharedAuthProvider> {
     if use_agent_identity_auth {
-        let agent_identity_jwt = read_codex_access_token_from_env().ok_or_else(|| {
+        read_codex_access_token_from_env().ok_or_else(|| {
             anyhow::anyhow!("CODEX_ACCESS_TOKEN is required when --use-agent-identity-auth is set")
         })?;
-        let auth_route_config = config.auth_route_config();
-        let auth = CodexAuth::from_agent_identity_jwt(
-            &agent_identity_jwt,
-            Some(&config.chatgpt_base_url),
-            &auth_route_config,
-        )
-        .await?;
+        let auth = AuthManager::shared_from_config(config, /*enable_codex_api_key_env*/ false)
+            .await
+            .auth()
+            .await
+            .ok_or_else(|| anyhow::anyhow!("Agent Identity authentication is unavailable"))?;
+        if !matches!(auth, CodexAuth::AgentIdentity(_)) {
+            anyhow::bail!(
+                "CODEX_ACCESS_TOKEN did not provide permitted Agent Identity authentication"
+            );
+        }
         return Ok(codex_model_provider::auth_provider_from_auth(&auth));
     }