feat(mcp): add browser OAuth for remote servers

docs/configuration.md

@@ -1971,15 +1971,52 @@ Add MCP servers to your `config.json`:
 }
 ```
 
-Two transport modes are supported:
+MCP servers can run locally over stdio or connect remotely over HTTP:
 
-| Mode | Config | Example |
+| Connection | Config | Example |
 |------|--------|---------|
 | **Stdio** | `command` + `args` | Local process via `npx` / `uvx` |
-| **HTTP** | `url` + `headers` (optional) | Remote endpoint (`https://mcp.example.com/sse`) |
+| **Streamable HTTP / SSE** | `url` + `headers` (optional) | Remote endpoint (`https://mcp.example.com/mcp`) |
+
+Remote HTTP servers may use browser OAuth instead of static headers. In the
+WebUI, open **Apps → MCP → Add MCP server**, choose **Custom**, select HTTP or
+SSE, and choose **OAuth** under **Authentication**. Save the server, then choose
+**Connect**. For manual configuration, add `auth: "oauth"` and open
+**Apps → MCP** to connect. Known presets such as Xmind, Notion, and Linear add
+the config automatically on first click.
+
+```json
+{
+  "tools": {
+    "mcpServers": {
+      "notion": {
+        "type": "streamableHttp",
+        "url": "https://mcp.notion.com/mcp",
+        "auth": "oauth"
+      }
+    }
+  }
+}
+```
+
+nanobot opens the server's authorization page and handles the callback through
+the gateway. The tools become available immediately when hot reload succeeds;
+otherwise the WebUI asks for a restart. OAuth tokens and dynamic client
+registration data are stored in the nanobot data directory under
+`auth/mcp.json`; they are not written to `config.json`. Removing the MCP server
+from Apps also removes its saved OAuth credentials. Normal gateway startup never
+opens a browser or registers a new OAuth client when credentials are
+missing—interactive authorization starts only after a user clicks **Connect**.
+
+For a remotely accessed WebUI, HTTPS is recommended. Configure
+`channels.websocket.publicWsUrl` with the browser-facing `wss://` endpoint so
+nanobot can register the matching HTTPS callback and finish automatically. A
+loopback WebUI may use HTTP. When a remote WebUI is served over plain HTTP,
+nanobot instead registers a localhost callback and asks you to paste the complete
+callback URL from the browser address bar after authorization.
 
 > [!IMPORTANT]
-> HTTP/SSE MCP URLs are validated before probing or connecting, and every outgoing MCP HTTP request is validated again before redirects are followed. `localhost`, `127.0.0.1`, RFC1918/private IPs, CGNAT/Tailscale ranges, link-local addresses, and cloud metadata endpoints are blocked by default. This can break previously working local or private HTTP MCP configs until the endpoint is explicitly allowed with `tools.ssrfWhitelist`, preferably with a single-host CIDR such as `127.0.0.1/32`, `::1/128`, or `192.168.1.50/32`. Stdio MCP servers are not affected.
+> HTTP/SSE MCP URLs are validated before probing or connecting, and every outgoing MCP HTTP request—including OAuth metadata, client registration, token exchange, and redirects—is validated again. `localhost`, `127.0.0.1`, RFC1918/private IPs, CGNAT/Tailscale ranges, link-local addresses, and cloud metadata endpoints are blocked by default. This can break previously working local or private HTTP MCP configs until the endpoint is explicitly allowed with `tools.ssrfWhitelist`, preferably with a single-host CIDR such as `127.0.0.1/32`, `::1/128`, or `192.168.1.50/32`. Stdio MCP servers are not affected.
 
 Use `toolTimeout` to override the default 30s per-call timeout for slow servers:
 

docs/guides/configure-mcp-tools.md

@@ -30,10 +30,15 @@ remote HTTP endpoint.
 For local interactive setup:
 
 1. Run `nanobot webui` and open **Apps**.
-2. Choose a known integration preset, or add a custom stdio, HTTP, or SSE server.
+2. Choose a known MCP server preset, or add a custom stdio, HTTP, or SSE server.
+   For a custom OAuth server, choose **OAuth** under **Authentication**, save it,
+   and click **Connect**. Presets such as Xmind, Notion, and Linear go straight to
+   **Connect**. Approve access in the browser window. HTTPS and localhost WebUIs
+   return automatically. From a remote plain-HTTP WebUI, copy the complete
+   localhost callback URL from the browser address bar and paste it into nanobot.
 3. Limit the enabled tools when the server exposes more than the task needs.
 4. Save and restart when prompted.
-5. Mention the integration with `@` in the next message and ask for a small test action.
+5. Mention the connected MCP server with `@` in the next message and ask for a small test action.
 
 For manual or deployment-managed config, add this to `~/.nanobot/config.json`:
 
@@ -58,12 +63,16 @@ Restart nanobot and ask a question that requires the MCP tool.
 - Prefer `enabledTools` over exposing every tool by default.
 - Use `toolTimeout` for slow MCP operations.
 - Use HTTP MCP only for endpoints you trust.
+- For deployment-managed OAuth servers, set `auth` to `oauth` and complete the
+  browser connection from **Apps → MCP**.
 - Keep MCP server commands stable and versioned in deployment docs or scripts.
 
 ## Security notes
 
 - Stdio MCP starts a local process; review the command before enabling it.
-- HTTP/SSE MCP uses nanobot's SSRF guard.
+- HTTP/SSE MCP uses nanobot's SSRF guard, including OAuth discovery, registration,
+  token exchange, and redirects.
+- OAuth credentials live in the nanobot data directory, not in `config.json`.
 - Allow private HTTP MCP hosts only with narrow `tools.ssrfWhitelist` CIDRs.
 - Do not place secrets in command arguments when environment variables or
   headers can be used.

docs/webui.md

@@ -204,8 +204,13 @@ turn. The default **Ready** view shows only tools that can be used immediately:
 - **Apps** are local command-line adapters that nanobot runs on your machine.
   Installing an adapter does not modify the native desktop or web app it
   connects to.
-- **Integrations** are MCP servers. Presets provide known configurations, and
-  the custom integration panel accepts stdio, HTTP, and SSE servers.
+- **MCP** lists Model Context Protocol servers. Presets provide known
+  configurations, and the **Add MCP server** panel accepts stdio, HTTP, and SSE
+  servers. Custom HTTP/SSE servers can use no authentication, OAuth, or request
+  headers. After saving an OAuth server, choose **Connect** to open its sign-in
+  page. Presets such as Xmind, Notion, and Linear already use OAuth. HTTPS and
+  localhost WebUIs return automatically; a remote plain-HTTP WebUI shows one
+  field for pasting the complete localhost callback URL.
 
 Apps intentionally does not list nanobot runtime support packages such as
 `api` or `bedrock`. Those packages enable providers, servers, or channels; they
@@ -226,8 +231,8 @@ endpoint and exposes `web_search` and `web_fetch` without requiring an API key.
 It is an optional integration and does not replace nanobot's built-in web search
 provider; mention `@parallel-search` when a turn should use it.
 
-After an App or integration is available, mention it from the composer with
-`@` to attach that tool to the next message.
+After an App or MCP server is available, mention it from the composer with `@`
+to attach that tool to the next message.
 
 ## Skills
 

nanobot/agent/tools/mcp.py

@@ -38,6 +38,7 @@
     from mcp.types import Prompt, Resource
     from mcp.types import Tool as MCPToolDefinition
 
+    from nanobot.agent.tools.mcp_oauth import MCPOAuthHandlers
     from nanobot.config.schema import MCPServerConfig
 
 # Transient connection errors that warrant a single retry.
@@ -184,6 +185,25 @@ def _is_transient(exc: BaseException) -> bool:
     return type(exc).__name__ in _TRANSIENT_EXC_NAMES
 
 
+def _is_transient_connection_failure(exc: BaseException) -> bool:
+    if isinstance(exc, BaseExceptionGroup):
+        group = cast(BaseExceptionGroup[BaseException], exc)
+        return bool(group.exceptions) and all(
+            _is_transient_connection_failure(nested) for nested in group.exceptions
+        )
+    return isinstance(exc, (httpx.ConnectError, httpx.ConnectTimeout)) or _is_transient(exc)
+
+
+def _log_mcp_connection_failure(name: str, exc: BaseException, hint: str = "") -> None:
+    if _is_transient_connection_failure(exc):
+        logger.warning("MCP server '{}': transient connection failure", name)
+        logger.opt(exception=exc).debug(
+            "MCP server '{}' transient connection failure details", name
+        )
+        return
+    logger.opt(exception=exc).error("MCP server '{}': failed to connect: {}", name, hint)
+
+
 def _is_session_terminated(exc: BaseException) -> bool:
     """Return True when the MCP SDK reports a dead client session."""
     if _is_transient(exc):
@@ -961,7 +981,10 @@ async def execute(self, **kwargs: Any) -> str:
 
 
 async def connect_mcp_servers(
-    mcp_servers: "dict[str, MCPServerConfig]", registry: ToolRegistry
+    mcp_servers: "dict[str, MCPServerConfig]",
+    registry: ToolRegistry,
+    *,
+    oauth_handlers: Mapping[str, "MCPOAuthHandlers"] | None = None,
 ) -> dict[str, MCPConnection]:
     """Connect to configured MCP servers and register their tools, resources, prompts.
 
@@ -1001,6 +1024,29 @@ async def open_single_server(
                     )
                     return False
 
+            oauth_auth: httpx.Auth | None = None
+            if cfg.auth == "oauth":
+                if transport_type not in {"sse", "streamableHttp"}:
+                    logger.warning(
+                        "MCP server '{}': OAuth requires an SSE or Streamable HTTP transport",
+                        name,
+                    )
+                    return False
+                from nanobot.agent.tools.mcp_oauth import (
+                    MCPAuthorizationRequiredError,
+                    create_mcp_oauth_auth,
+                )
+
+                try:
+                    oauth_auth = await create_mcp_oauth_auth(
+                        name,
+                        cfg.url,
+                        (oauth_handlers or {}).get(name),
+                    )
+                except MCPAuthorizationRequiredError:
+                    logger.info("MCP server '{}': waiting for browser authorization", name)
+                    return False
+
             if transport_type == "stdio":
                 command, args, env = _normalize_windows_stdio_command(
                     cfg.command,
@@ -1038,22 +1084,30 @@ def httpx_client_factory(
                         **_pinned_transport_kwargs(),
                     )
 
+                sse_kwargs: dict[str, Any] = {
+                    "httpx_client_factory": httpx_client_factory,
+                }
+                if oauth_auth is not None:
+                    sse_kwargs["auth"] = oauth_auth
                 read, write = await server_stack.enter_async_context(
-                    sse_client(cfg.url, httpx_client_factory=httpx_client_factory)
+                    sse_client(cfg.url, **sse_kwargs)
                 )
             elif transport_type == "streamableHttp":
                 if not await _probe_http_url(cfg.url):
                     logger.warning("MCP server '{}': {} unreachable, skipping", name, _redact_url(cfg.url))
                     return False
 
+                http_client_kwargs: dict[str, Any] = {
+                    "headers": cfg.headers or None,
+                    "event_hooks": {"request": [_validate_mcp_request_url]},
+                    "follow_redirects": True,
+                    "timeout": httpx.Timeout(30.0, connect=10.0),
+                    **_pinned_transport_kwargs(),
+                }
+                if oauth_auth is not None:
+                    http_client_kwargs["auth"] = oauth_auth
                 http_client = await server_stack.enter_async_context(
-                    httpx.AsyncClient(
-                        headers=cfg.headers or None,
-                        event_hooks={"request": [_validate_mcp_request_url]},
-                        follow_redirects=True,
-                        timeout=httpx.Timeout(30.0, connect=10.0),
-                        **_pinned_transport_kwargs(),
-                    )
+                    httpx.AsyncClient(**http_client_kwargs)
                 )
                 read, write, _ = await server_stack.enter_async_context(
                     streamable_http_client(cfg.url, http_client=http_client)
@@ -1182,7 +1236,7 @@ def httpx_client_factory(
                     " Hint: this looks like stdio protocol pollution. Make sure the MCP server writes "
                     "only JSON-RPC to stdout and sends logs/debug output to stderr instead."
                 )
-            logger.exception("MCP server '{}': failed to connect: {}", name, hint)
+            _log_mcp_connection_failure(name, e, hint)
             return False
 
     async def connect_single_server(
@@ -1229,7 +1283,7 @@ async def own_connection() -> None:
         try:
             result = await connect_single_server(name, cfg)
         except Exception as e:
-            logger.exception("MCP server '{}' connection failed: {}", name, e)
+            _log_mcp_connection_failure(name, e)
             continue
         if result[1] is not None:
             server_stacks[result[0]] = result[1]
@@ -1302,6 +1356,13 @@ async def reload_servers(state: Any, registry: ToolRegistry) -> dict[str, Any]:
         current_servers = dict(state._mcp_servers)
         current_names = set(current_servers)
         next_names = set(next_servers)
+        from nanobot.agent.tools.mcp_oauth import mcp_oauth_has_credentials
+
+        authorization_pending = {
+            name
+            for name, cfg in next_servers.items()
+            if cfg.auth == "oauth" and not mcp_oauth_has_credentials(name, cfg.url)
+        }
         removed = sorted(current_names - next_names)
         added = sorted(next_names - current_names)
         changed = sorted(
@@ -1319,9 +1380,13 @@ async def reload_servers(state: Any, registry: ToolRegistry) -> dict[str, Any]:
         retry_missing = sorted(
             name
             for name in next_names
-            if name not in state._mcp_stacks and name not in set(added) | set(changed)
+            if name not in state._mcp_stacks
+            and name not in set(added) | set(changed)
+            and name not in authorization_pending
+        )
+        to_connect_names = sorted(
+            (set(added) | set(changed) | set(retry_missing)) - authorization_pending
         )
-        to_connect_names = sorted(set(added) | set(changed) | set(retry_missing))
         to_connect = {name: next_servers[name] for name in to_connect_names}
         connected: dict[str, MCPConnection] = {}
         if to_connect: