Harden MCP OAuth callback handling (#40691)

## Why

MCP servers can share an OAuth callback URL. Without a validated issuer or a
server-specific callback path, an authorization response could be associated
with the wrong server.

## What changed

- Use stable callbacks when authorization metadata advertises issuer-bound
  responses, and validate the returned issuer before exchanging the code.
- Retain server-specific callback IDs for providers without issuer support,
  including fallback to the global or default callback for legacy registered
  clients.
- Persist registered callback URLs for MCP servers and plugins, and insert the
  active listener port into portless loopback redirects.

## Testing

Add coverage for issuer validation, callback-mode discovery, registered and
legacy clients, plugin OAuth, CLI persistence, and loopback listener ports.

GitOrigin-RevId: 2878c92e237fc17fd3def0bd2e1cce3e104a3db8

codex-rs/app-server/src/request_processors/plugins.rs

@@ -28,6 +28,7 @@ use codex_core_plugins::remote_bundle::RemotePluginBundleInstallError;
 use codex_mcp::McpOAuthLoginSupport;
 use codex_mcp::McpRuntimeContext;
 use codex_mcp::oauth_login_support;
+use codex_mcp::resolve_oauth_callback;
 use codex_mcp::should_retry_without_scopes;
 use codex_plugin::PluginId;
 use codex_plugin::PluginTelemetryMetadata;
@@ -1943,12 +1944,25 @@ impl PluginRequestProcessor {
             let store_mode = config.mcp_oauth_credentials_store_mode;
             let keyring_backend_kind = config.auth_keyring_backend_kind();
             let callback_port = server.oauth_callback_port(config.mcp_oauth_callback_port);
-            let callback_url = config.mcp_oauth_callback_url.clone();
+            let callback_url = match resolve_oauth_callback(
+                &server,
+                &oauth_config.url,
+                config.mcp_oauth_callback_url.as_deref(),
+            ) {
+                Ok(callback_url) => callback_url,
+                Err(error) => {
+                    warn!(
+                        "failed to resolve MCP OAuth callback for plugin install {name}: {error}"
+                    );
+                    continue;
+                }
+            };
             let outgoing = Arc::clone(&self.outgoing);
             let notification_name = name.clone();
             let oauth_credential_name = server.oauth_credential_name(&name).into_owned();
             let thread_manager = Arc::clone(&self.thread_manager);
             let http_client = Arc::clone(&http_client);
+            let global_callback_url = config.mcp_oauth_callback_url.clone();
 
             tokio::spawn(async move {
                 let oauth_client_id = server.oauth_client_id();
@@ -1965,6 +1979,7 @@ impl PluginRequestProcessor {
                     server.oauth_resource.as_deref(),
                     callback_port,
                     callback_url.as_deref(),
+                    global_callback_url.as_deref(),
                     Arc::clone(&http_client),
                     redirect_mode,
                 )
@@ -1985,6 +2000,7 @@ impl PluginRequestProcessor {
                             server.oauth_resource.as_deref(),
                             callback_port,
                             callback_url.as_deref(),
+                            global_callback_url.as_deref(),
                             http_client,
                             redirect_mode,
                         )