[model-gateway] Avoid logging MCP connection token (#13887)

sgl-router/src/mcp/config.rs

@@ -2,7 +2,7 @@
 //!
 //! Defines configuration structures for MCP servers, transports, proxies, and inventory.
 
-use std::collections::HashMap;
+use std::{collections::HashMap, fmt};
 
 pub use rmcp::model::{Prompt, RawResource, Tool};
 use serde::{Deserialize, Serialize};
@@ -48,7 +48,7 @@ pub struct McpServerConfig {
     pub required: bool,
 }
 
-#[derive(Debug, Clone, Deserialize, Serialize)]
+#[derive(Clone, Deserialize, Serialize)]
 #[serde(tag = "protocol", rename_all = "lowercase")]
 pub enum McpTransport {
     Stdio {
@@ -70,6 +70,33 @@ pub enum McpTransport {
     },
 }
 
+impl fmt::Debug for McpTransport {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            McpTransport::Stdio {
+                command,
+                args,
+                envs,
+            } => f
+                .debug_struct("Stdio")
+                .field("command", command)
+                .field("args", args)
+                .field("envs", envs)
+                .finish(),
+            McpTransport::Sse { url, token } => f
+                .debug_struct("Sse")
+                .field("url", url)
+                .field("token", &token.as_ref().map(|_| "****"))
+                .finish(),
+            McpTransport::Streamable { url, token } => f
+                .debug_struct("Streamable")
+                .field("url", url)
+                .field("token", &token.as_ref().map(|_| "****"))
+                .finish(),
+        }
+    }
+}
+
 /// MCP-specific proxy configuration (does NOT affect LLM API traffic)
 #[derive(Debug, Clone, Deserialize, Serialize)]
 pub struct McpProxyConfig {