mcp-gateway

Vengtoo MCP Gateway

  

Authorization gateway for AI agents and MCP tool calls.

Open-source. Drop-in. Works with any MCP client.

Why

AI agents connected to MCP servers can call any tool they have access to — read your database, delete files, execute arbitrary SQL. Vengtoo MCP Gateway puts a policy enforcement point between the agent and those tools, so every call is authorized before it executes.

What it does

• Sits between MCP clients (Claude Code, Cursor, VS Code, GitHub Copilot) and any MCP server
• Intercepts every tool call and checks authorization before forwarding
• Two modes: cloud (Vengtoo Cloud API) and local (Vengtoo Agent + .rego policy file)
• Full audit trail of every tool invocation — subject, tool name, arguments, and decision are logged as structured JSON:

{"ts":"2026-05-25T10:03:11.482Z","level":"info","msg":"mcp_tool_call","subject":"agent:ai-assistant","tool":"database__query","allowed":true,"latency_ms":0.8}

Quick Start

1. Install and start the Vengtoo Agent. The agent runs locally and evaluates your authorization policy — no cloud account needed.

go install github.com/vengtoo/agent/cmd/agent@latest
vengtoo-agent --policy ./policy.rego

Create a policy.rego to define what your agent can do:

package vengtoo.mcp

default allow := false

# Allow read-only tools
allow if { input.resource.name == "database__query" }
allow if { input.resource.name == "database__list_tables" }

# Allow writes, but block destructive SQL
allow if {
    input.resource.name == "database__execute"
    not contains(lower(input.resource.attributes.sql), "drop")
    not contains(lower(input.resource.attributes.sql), "delete from")
}

See demo/policies/ for more examples including Kubernetes namespace protection.

1. Create a gateway.config.json:

{
  "vengtoo": {
    "agentUrl": "http://localhost:8181"
  },
  "subject": "agent:ai-assistant",
  "servers": {
    "database": {
      "command": "node",
      "args": ["./my-database-mcp-server.js"]
    }
  }
}

1. Add to your MCP client (e.g. Claude Code):

claude mcp add --transport stdio vengtoo-gateway -- \
  npx vengtoo-mcp-gateway --config /path/to/gateway.config.json

Configuration

Config schema

| Field | Type | Required | Description | | ------------------ | ------ | -------- | -------------------------------------------------------------- | | vengtoo.agentUrl | string | \ | URL of local Vengtoo Agent (local mode) | | vengtoo.cloudUrl | string | \ | URL of Vengtoo Cloud API (cloud mode) | | vengtoo.apiKey | string | | API key from Vengtoo Cloud (or set VENGTOO_API_KEY env var) | | vengtoo.timeoutMs | number | | Authorization request timeout (default: 5000) | | subject | string | yes | Identity of the agent making tool calls | | subjectType | string | | Subject type (default: "agent") | | resourceType | string | | Resource type for authorization checks (default: "mcp_tool") | | servers | object | yes | Map of downstream MCP servers to proxy |

\* Provide either agentUrl (local mode) or cloudUrl (cloud mode).

Each entry in servers has:

| Field | Type | Required | Description | | --------- | -------- | -------- | -------------------------------- | | command | string | yes | Command to spawn the MCP server | | args | string[] | | Command arguments | | env | object | | Additional environment variables |

Modes

Cloud mode

Connect to Vengtoo Cloud for managed policies:

{
  "vengtoo": {
    "cloudUrl": "https://api.vengtoo.com/access/v1/evaluation",
    "apiKey": "azx_..."
  },
  "subject": "agent:prod-assistant",
  "servers": {
    "database": {
      "command": "node",
      "args": ["./db-server.js"]
    }
  }
}

Local mode

Run the Vengtoo Agent locally with a .rego policy file for offline, self-contained authorization:

# Start the agent with your policy
vengtoo-agent --policy ./policy.rego

{
  "vengtoo": {
    "agentUrl": "http://localhost:8181"
  },
  "subject": "agent:dev-assistant",
  "servers": {
    "database": {
      "command": "node",
      "args": ["./db-server.js"]
    }
  }
}

CLI Flags

| Flag | Description | | -------------------------- | -------------------------------------------------------------------------------------- | | --config <path> | Path to gateway config file (default: ./gateway.config.json) | | --list-tools | List all tools from configured downstream servers and exit | | --generate-policy [path] | Generate a starter .rego policy file for the configured tools (default: policy.rego) |

Environment variable overrides: VENGTOO_API_KEY, VENGTOO_AGENT_URL, AUTHZX_SUBJECT.

MCP Client Setup

The gateway runs as a stdio MCP server. Point your MCP client at it instead of the downstream server directly.

Claude Code

claude mcp add --transport stdio vengtoo-gateway -- \
  npx vengtoo-mcp-gateway --config /path/to/gateway.config.json

Cursor

Add to .cursor/mcp.json:

{
  "mcpServers": {
    "vengtoo-gateway": {
      "command": "npx",
      "args": ["vengtoo-mcp-gateway", "--config", "/path/to/gateway.config.json"]
    }
  }
}

Claude Desktop

Add to ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "vengtoo-gateway": {
      "command": "npx",
      "args": ["vengtoo-mcp-gateway", "--config", "/path/to/gateway.config.json"]
    }
  }
}

VS Code / GitHub Copilot

Add to .vscode/mcp.json:

{
  "servers": {
    "vengtoo-gateway": {
      "type": "stdio",
      "command": "npx",
      "args": ["vengtoo-mcp-gateway", "--config", "/path/to/gateway.config.json"]
    }
  }
}

See demo/ for full end-to-end examples with sample policies.

Feedback

• GitHub Issues — Bug reports and feature requests
• Documentation — Guides and API reference

License

Apache-2.0 — see LICENSE.