@mcp-abap-adt/proxy

v5.0.3

Published

18 days ago

MCP proxy server for SAP ABAP ADT - proxies local requests to cloud-llm-hub with JWT authentication

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abap sap adt mcp model-context-protocol proxy

@mcp-abap-adt/proxy

MCP proxy server for SAP ABAP ADT - proxies local requests to MCP servers with JWT authentication.

Overview

This package acts as a simple proxy between local MCP clients (like Cline) and any MCP server. It intercepts MCP requests, adds JWT authentication tokens, and forwards them to the target MCP server. The MCP server URL is obtained from the service key for the BTP destination.

Purpose

Enable local MCP clients to connect to remote MCP servers with automatic JWT token management via @mcp-abap-adt/auth-broker. The proxy adds authentication headers and forwards requests transparently.

Features

✅ One shared credential - the token is the auth-broker's business: it caches, knows expiry and renews behind the call. The proxy holds no token of its own
✅ Service Key Based - MCP server URL is obtained from service key for BTP destination
✅ Transparent forwarding - the client's headers go through as sent; the proxy answers for the Authorization header and nothing else
✅ Error Handling - token acquisition is retried with exponential backoff when the failure can get better; clear messages when it cannot
✅ Multiple Transport Modes - HTTP, SSE, and stdio support
✅ Configuration Flexibility - Environment variables, config files, or defaults

Quick Start

Installation

npm install -g @mcp-abap-adt/proxy

Basic Usage

# Start proxy server (in-memory session storage, secure)
mcp-abap-adt-proxy

# With BTP destination
mcp-abap-adt-proxy --btp=ai

# Enable file-based session storage (persists tokens to disk)
mcp-abap-adt-proxy --btp=ai --unsafe

Two commands

The package installs two binaries, for two different jobs.

| Command | What it is for | |---|---| | mcp-abap-adt-proxy | Be a proxy. A client points at it and its requests are authenticated and forwarded. | | mcp-abap-adt-proxy-mcp | Manage proxies. Speaks MCP over stdio; its tools start and stop proxies on demand. |

The management mode

{
  "mcpServers": {
    "abap-proxy": { "command": "mcp-abap-adt-proxy-mcp" }
  }
}

It works from the proxy configs you already keep:

~/.config/mcp-abap-adt/proxy/<name>.yaml     (Windows: Documents\mcp-abap-adt\proxy\)

These are the same files mcp-abap-adt-proxy --config <file> takes. Starting a proxy is therefore choosing a name, not assembling settings — and credentials stay in the config, resolved through ${VAR} interpolation, rather than travelling through a tool call.

| Tool | What it does | |---|---| | proxy_configs | Lists the configs available, by the name proxy_start takes. Call it first — the names cannot be guessed. | | proxy_environments | Lists the environments available — one SAP system's credentials each, by the name proxy_start takes. Variable NAMES only, never values. | | proxy_start | Starts a proxy from a config and, when the config needs one, an environment. Returns the URL it bound. The port is not taken from the config: a free one is bound instead. | | proxy_stop | Stops a proxy this session started, freeing its port and releasing its credential. Proxies started by other sessions are never touched. | | proxy_status | Lists this session's proxies and any others on this machine. Records whose process has died are pruned when read, so it cannot report a ghost. |

The config name is the unit, not the destination. Several configs commonly name the same btpDestination and differ in target URL and headers — a destination cannot tell them apart.

Every proxy runs inside the management process. Closing the session — or SIGINT, or SIGTERM — stops all of them and frees their ports. This is deliberate: a spawned child would be orphaned by any signal the parent did not forward and would go on holding its HTTP and OAuth callback ports.

A proxy nobody has used for 30 minutes stops itself. That is a backstop for a client that finished and forgot, not a substitute for proxy_stop — which is why the tool descriptions say so, and say it again beside the URL.

Configuration

The proxy supports multiple configuration methods:

Command-line parameters (highest priority)
YAML/JSON configuration files - See YAML Configuration Guide
Environment variables
Default values (lowest priority)

Quick Example (YAML config):

# Copy example config from documentation
cp docs/mcp-proxy-config.example.yaml mcp-proxy-config.yaml

# Edit mcp-proxy-config.yaml with your settings

# Run with config file
mcp-abap-adt-proxy --config=mcp-proxy-config.yaml
# Or short form:
mcp-abap-adt-proxy -c mcp-proxy-config.yaml

Client Configuration

For detailed setup instructions for Cline and GitHub Copilot, see the Client Setup Guide.

Quick Example (Cline):

{
  "mcpServers": {
    "mcp-abap-adt-proxy": {
      "disabled": false,
      "timeout": 60,
      "type": "streamableHttp",
      "url": "http://localhost:3001/mcp/stream/http",
      "headers": {
        "x-sap-destination": "btp-cloud"
      }
    }
  }
}

Required Headers:

x-sap-destination - Destination name for BTP Cloud authorization token and MCP server URL

Command Line Overrides:

--btp=<destination> - Overrides x-sap-destination header (takes precedence)
--url=<url> - Overrides MCP server URL (required if service key lacks URL)
--browser=<browser> - Browser to use: system (default), chrome, edge, firefox, headless
--browser-auth-port=<port> - Port for the OAuth2 callback (default: 3333). Bound only while you are logging in, then released — see How long the callback port is held
--unsafe - Enables file-based session storage (persists tokens to disk). By default, sessions are stored in-memory (secure, lost on restart)

Default Headers:

MCP clients like Cline and Claude Code cannot set arbitrary request headers. Use default headers to inject SAP-specific headers (e.g. x-sap-destination, x-sap-client) that the target MCP server requires.

Precedence: client-supplied request headers always win over defaultHeaders. Authorization is the exception — it is always managed by the proxy (replaced with the destination JWT) and cannot be set via defaultHeaders.

Via YAML config (defaultHeaders map):

btpDestination: mcp
targetUrl: https://example.com
defaultHeaders:
  x-sap-destination: S4HANA_E19
  x-sap-client: "100"

Per-user ABAP credentials. defaultHeaders is the supported place to supply your own SAP login/password for on-premise / NoAuthentication destinations. The upstream cloud-llm-hub is a shared server with no default service user, so it expects each caller's own x-sap-login / x-sap-password on every request. Because the proxy runs locally on each user's machine, it carries your identity.

Do not hardcode secrets. Reference environment variables with ${VAR} (or ${VAR:-default}); values are resolved from process.env or an explicitly-pointed .env file:

btpDestination: mcp
envFile: secrets.env            # resolved relative to this config file's dir
defaultHeaders:
  x-sap-destination: S4HANA_E19
  x-sap-login: ${SAP_USER}
  x-sap-password: ${SAP_PASSWORD}

secrets.env (user-local, chmod 600, never committed):

SAP_USER=MY_SAP_USER
SAP_PASSWORD=my-sap-password

Resolution order is process.env → .env → ${VAR:-default}. process.env wins; an unresolved ${VAR} without a default fails the proxy at startup. Override the .env path at launch with --env-file <path>. This closes both auth layers from one local config: the service layer (Authorization: Bearer <JWT>, from the destination service key) and the ABAP layer (x-sap-login / x-sap-password).

Via CLI (--header, repeatable):

mcp-abap-adt-proxy --btp=mcp --url=https://example.com \
  --header x-sap-destination=S4HANA_E19 \
  --header x-sap-client=100

How It Works:

The proxy uses BTP/XSUAA authentication:

BTP Authentication (if --btp or x-sap-destination is present):
- Uses AuthorizationCodeProvider (browser-based OAuth2 flow)
- Eager Authentication: Opens browser immediately on startup to get token
- Injects/overwrites Authorization: Bearer <token> header
- MCP server URL obtained from BTP destination service key OR injected via --url
- Service key format: contains uaa (url, clientid, clientsecret)

BTP Authentication Mode (with --btp):

Proxy starts → Opens browser for login (Eager Auth) → Gets/Refreshes JWT token
x-sap-destination (or --btp) → Adds Authorization: Bearer <token> header
MCP server URL obtained from service key OR --url parameter

Documentation

🚚 Migration to 4.0 — the contracts leave the umbrella, an SSE response streams and carries your headers, getJwtToken() is replaced, the circuit breaker is gone
Client Setup Guide - Step-by-step setup for Cline and GitHub Copilot
Configuration Guide - Complete configuration reference
YAML Configuration Guide - Using YAML/JSON configuration files
Usage Examples - Practical usage examples and patterns
API Documentation - API reference and interfaces
Architecture - System architecture and design
Troubleshooting - Common issues and solutions
Routing Logic Specification - Detailed routing logic and scenarios
Roadmap - Development roadmap and progress

How It Works

The proxy performs the following steps for each request:

Extract Headers: Reads x-sap-destination header
Apply Command Line Overrides: --btp parameter overrides header (if provided)
Validate Routing Requirements: Requires x-sap-destination/--btp
BTP Authentication (if x-sap-destination or --btp is provided):
- Uses AuthorizationCodeProvider (browser-based login)
- Eagerly obtains token on startup (if configured via --btp)
- Retrieves JWT token using cached refresh token or opens browser
- Injects/overwrites Authorization: Bearer <token> header
Get MCP Server URL:
- From service key for x-sap-destination
Forward Request: Sends request to MCP server URL with all injected headers
Return Response: Forwards the response back to the client

Example Request Flow

Cline → Proxy (adds BTP token) → Target MCP Server → Proxy → Cline

The proxy is transparent - it only adds authentication headers and forwards requests.

Configuration

Environment Variables

export MCP_HTTP_PORT=3001
export LOG_LEVEL=info
export MCP_PROXY_UNSAFE=true  # Enable file-based session storage (optional)
export AUTH_BROKER_PATH=~/.config/mcp-abap-adt  # Optional base path for service-keys/sessions

AUTH_BROKER_PATH is treated as a base directory. The proxy resolves:

service-keys from <AUTH_BROKER_PATH>/service-keys
sessions from <AUTH_BROKER_PATH>/sessions

Defaults when AUTH_BROKER_PATH is not set:

Unix/Linux/macOS: ~/.config/mcp-abap-adt/service-keys and ~/.config/mcp-abap-adt/sessions
Windows: %USERPROFILE%\\Documents\\mcp-abap-adt\\service-keys and %USERPROFILE%\\Documents\\mcp-abap-adt\\sessions

Configuration File

Create mcp-proxy-config.json:

{
  "httpPort": 3001,
  "logLevel": "info",
  "maxRetries": 3,
  "unsafe": false
}

Session Storage:

unsafe: false (default) - Session data stored in-memory (secure, lost on restart)
unsafe: true - Session data persisted to disk (tokens saved under the session store path): the service URL, the token and the refresh token. The client secret is not copied there; it stays in the service key

See Configuration Guide for complete options.

Error Handling & Resilience

Retry Logic - exponential backoff while getting a token, for failures that can get better (5xx, network). A missing service key is not one of them and fails at once, with a message naming the file to create
Token Refresh - handled by the credential, which is asked per request and renews behind the call
No circuit breaker - it guarded the buffered forward that 4.0.0 removed. The forwarding path now streams, and there is nowhere to put one without buffering the response again. circuitBreakerThreshold and circuitBreakerTimeout are still accepted so existing configs load, and do nothing
Request Timeouts - Configurable timeout handling

Requirements

Node.js 22, 24 or 26 (engines: "^22 || ^24 || ^26", as @mcp-abap-adt/auth-providers)
npm >= 9.0.0

Testing Tools

Verify a BTP destination's service key and token retrieval:

npm run test-destination -- <destination>

See tools/README.md for the available scripts.

Development Status

✅ Core Features Complete

✅ Project Setup & Foundation
✅ Request Interception & Analysis
✅ JWT Token Management & Proxy Forwarding
✅ Configuration & Environment
✅ Error Handling & Resilience
✅ Testing Tools (tools/)
✅ Documentation

🚧 Future Work

⏳ Unit Tests
⏳ Performance & Optimization
⏳ Deployment & Publishing

See ROADMAP.md for details.

License

GNU General Public License v3.0 only (GPL-3.0-only). Earlier published versions were MIT and stay MIT — a licence change is not retroactive.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 3.

It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See LICENSE for the full text.

What this means. Running it, and using it on your own data, carries no conditions at all. Distributing it, or a modified version of it, means passing on the same freedoms — including the source. This is a finished tool rather than a library to build on; the libraries it is built from are LGPL, so they can be linked from programs under any licence.

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Readme

@mcp-abap-adt/proxy

Overview

Purpose

Features

Quick Start

Installation

Basic Usage

Two commands

The management mode

Configuration

Client Configuration

Documentation

How It Works

Example Request Flow

Configuration

Configuration

Environment Variables

Configuration File

Error Handling & Resilience

Requirements

Testing Tools

Development Status

License

Links