Sameer Kankute 18f77ff7bc feat(mcp): add delegate_auth_to_upstream flag for PKCE passthrough (#27834)
* feat(mcp): add delegate_auth_to_upstream flag for PKCE passthrough

Adds an opt-in per-server flag that lets clients (e.g. VS Code) complete
PKCE directly with an upstream OAuth2 MCP server, instead of LiteLLM
double-gating with its own API-key/SSO check. Only honored when
auth_type=oauth2 and the operator explicitly sets the flag; mixed-target
or non-oauth2 requests fail closed.

- Adds the field to Pydantic models, Prisma schema, and a migration
- New MCPRequestHandler._target_servers_delegate_auth_to_upstream gate
  that runs only when no x-litellm-api-key is present, so authenticated
  users still get user_id resolution + stored-credential lookup
- Anonymous callers now see delegate servers in get_allowed_mcp_servers
  (scoped to delegate servers only; the upstream still enforces auth)
- mcp_management_endpoints: allow anonymous /authorize and /token for
  delegate servers so VS Code can complete PKCE without a LiteLLM session
- UI toggle (shown only for oauth2) + payload/view wiring
- Tests covering: oauth2 on/off, non-oauth2 with flag, mixed targets,
  no resolvable target, explicit key precedence, and 401 emission

Co-authored-by: Cursor <cursoragent@cursor.com>

* Enforce oauth2 for delegated MCP auth bypass

Co-authored-by: Yassin Kortam <yassin@berri.ai>

* fix(mcp): close secondary Authorization bypass for delegate servers

The delegate-auth bypass gated only on the primary `x-litellm-api-key`
header, so a LiteLLM key sent via `Authorization: Bearer sk-...` (the
secondary header) was silently dropped — skipping spend tracking and
rate limiting. Gate on the resolved litellm_api_key (which considers
both headers) so the bypass fires only when neither is present.

Also update the existing "Authorization header present" test to reflect
that an upstream OAuth token now flows through the existing oauth2
fallback (LiteLLM auth attempt → fail → anonymous), not via the
delegate branch.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Avoid duplicate MCP OAuth credential lookup

Co-authored-by: Yassin Kortam <yassin@berri.ai>

* fix(mcp): block delegate bypass for M2M and internal-only servers

Two security issues flagged in code review:

1. High – client_credentials (M2M) servers must not be delegatable:
   LiteLLM auto-fetches the upstream token using stored credentials, so
   allowing anonymous bypass would let any external caller invoke tools
   authenticated as LiteLLM's service account.
   Fix: check `server.has_client_credentials` in
   `_target_servers_delegate_auth_to_upstream`, the anonymous
   allow-list in `get_allowed_mcp_servers`, and `_mcp_oauth_user_api_key_auth`.

2. Medium – internal-only servers exposed to public internet:
   The anonymous delegate allow-list was not filtering by
   `available_on_public_internet`, so external callers with an upstream
   OAuth token could invoke tools on servers marked internal-only.
   Fix: add `available_on_public_internet` guard to the anonymous
   delegate server list in `get_allowed_mcp_servers`.

Tests added for both cases.

Co-authored-by: Cursor <cursoragent@cursor.com>

* Require public MCP delegate auth servers

Co-authored-by: Yassin Kortam <yassin@berri.ai>

* fix(mcp): align delegate auth path parsing with downstream routing

`_extract_target_server_names_from_path` used a naive segments-based
split while `server.py::_get_mcp_servers_in_path` uses a regex that
allows server names with one embedded slash and comma-separated lists.
With the old parser, a request to `/mcp/<delegated>/<garbage>` was
parsed as targeting `<delegated>` by the auth gate (bypassing LiteLLM
auth) while the routing layer parsed it as `<delegated>/<garbage>` —
when that name did not resolve, the request fell back to the anonymous
allow-list, which can include `allow_all_keys` servers that normally
require a LiteLLM key.

Replace the parser with the same regex logic as
`_get_mcp_servers_in_path` so auth gating sees the exact target name(s)
downstream routing sees. Add regression tests covering parser parity
and the specific extra-path-segment bypass attempt.

https://claude.ai/code/session_01SjyPmwfmrq8fveFgw9iHW9

* fix(mcp): close header/path TOCTOU in MCP delegate auth gate

`_target_servers_delegate_auth_to_upstream` and
`_target_servers_use_oauth2` trusted the `x-mcp-servers` header when
present, but `server.py::extract_mcp_auth_context` overrides that
header with the path-derived list for `/mcp/...` routes. An attacker
could set `x-mcp-servers: <delegated>` while pointing the URL path at
a non-delegate server, flipping the auth gate without changing the
target downstream routing actually uses.

Extract a shared `_resolve_target_server_names` helper that mirrors
the downstream override (path-derived names for `/mcp/...` routes,
header value otherwise). Add regression tests covering the TOCTOU
attempt and the helper's path-vs-header precedence.

https://claude.ai/code/session_01SjyPmwfmrq8fveFgw9iHW9

* Fix delegated MCP OAuth test mock

Co-authored-by: Yassin Kortam <yassin@berri.ai>

* fix(mcp): drop unreachable /{server}/mcp branch in auth path parser

`_extract_target_server_names_from_path` also matched the
``/{server_name}/mcp`` form, but the downstream parser
``_get_mcp_servers_in_path`` only handles ``/mcp/...`` — and
``dynamic_mcp_route`` in ``proxy_server`` rewrites ``/{name}/mcp``
to ``/mcp/{name}`` on the scope before the MCP handler runs. Parsing
the un-rewritten form on the auth side was therefore unreachable in
production, and contradicted the docstring's claim of mirroring the
downstream parser — exactly the kind of mismatch that risks a future
header/path TOCTOU if any new entry point skips the rewrite.

Drop the branch; the canonical ``/mcp/...`` path matches both
parsers. Update the regression test to assert the new behavior.

https://claude.ai/code/session_01SjyPmwfmrq8fveFgw9iHW9

* Fix MCP path auth target resolution

Co-authored-by: Yassin Kortam <yassin@berri.ai>

* fix(mcp): require auth for refresh_token grants on delegate-auth servers

`_mcp_oauth_user_api_key_auth` gates the unauthenticated PKCE flow for
``delegate_auth_to_upstream`` servers, but the bypass applied to BOTH
``/authorize`` and ``/token`` regardless of grant type. ``mcp_token``
accepts ``grant_type=refresh_token`` as well as ``authorization_code``,
and ``exchange_token_with_server`` attaches the server's stored
``client_secret`` to whatever is forwarded upstream. An unauthenticated
caller holding a refresh token issued to that OAuth client could mint
fresh upstream access tokens through LiteLLM.

Limit the anonymous bypass on ``/token`` to ``grant_type=authorization_code``
(the only grant PKCE actually protects via ``code_verifier``); fall
through to normal LiteLLM auth for ``refresh_token`` and any other grant.
``/authorize`` continues to allow anonymous PKCE redirects.

https://claude.ai/code/session_01SjyPmwfmrq8fveFgw9iHW9

* fix(ui): clear delegate_auth_to_upstream when switching off oauth2

The ``delegate_auth_to_upstream`` form field is rendered inside an
``isOAuth2 && (...)`` conditional, so the Form.Item unmounts when the
user changes ``auth_type`` away from ``oauth2``. The follow-up
``form.setFieldValue("delegate_auth_to_upstream", false)`` runs after
the field has already deregistered, so ``onFinish`` receives
``undefined`` and the fallback ``?? mcpServer.delegate_auth_to_upstream``
preserved the old ``true``. The flag then persisted in the database for
a non-oauth2 server and silently re-activated if ``auth_type`` was later
switched back to ``oauth2``.

In the edit payload, force the flag to ``false`` whenever
``auth_type !== oauth2``; only trust the form value (and the existing
DB fallback) when the server is actually oauth2. Backend defense-in-depth
already ignores the flag for non-oauth2 servers, but the DB state should
stay clean too.

https://claude.ai/code/session_01SjyPmwfmrq8fveFgw9iHW9

* Fix MCP delegate auth reset on edit

Co-authored-by: Yassin Kortam <yassin@berri.ai>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Yassin Kortam <yassin@berri.ai>
Co-authored-by: Claude <claude@anthropic.com>
2026-05-13 12:06:13 -07:00

🚅 LiteLLM

LiteLLM AI Gateway

Open Source AI Gateway for 100+ LLMs. Self-hosted. Enterprise-ready. Call any LLM in OpenAI format.

Deploy to Render Deploy on Railway

LiteLLM Proxy Server (AI Gateway) | Hosted Proxy | Enterprise Tier | Website

PyPI Version GitHub Stars Y Combinator W23 Whatsapp Discord Slack CodSpeed

Group 7154 (1)

What is LiteLLM

LiteLLM is an open source AI Gateway that gives you a single, unified interface to call 100+ LLM providers — OpenAI, Anthropic, Gemini, Bedrock, Azure, and more — using the OpenAI format.

Use it as a Python SDK for direct library integration, or deploy the AI Gateway (Proxy Server) as a centralized service for your team or organization.

Jump to LiteLLM Proxy (LLM Gateway) Docs
Jump to Supported LLM Providers


Why LiteLLM

Managing LLM calls across providers gets complicated fast — different SDKs, auth patterns, request formats, and error types for every model. LiteLLM removes that friction:

  • Unified API — one interface for 100+ LLMs, no provider-specific SDK juggling
  • Drop-in OpenAI compatibility — swap providers without rewriting your code
  • Production-ready gateway — virtual keys, spend tracking, guardrails, load balancing, and an admin dashboard out of the box
  • 8ms P95 latency at 1k RPS (benchmarks)

OSS Adopters

Stripe image Google ADK Greptile OpenHands

Netflix

OpenAI Agents SDK

Features

LLMs - Call 100+ LLMs (Python SDK + AI Gateway)

All Supported Endpoints - /chat/completions, /responses, /embeddings, /images, /audio, /batches, /rerank, /a2a, /messages and more.

Python SDK

uv add litellm
from litellm import completion
import os

os.environ["OPENAI_API_KEY"] = "your-openai-key"
os.environ["ANTHROPIC_API_KEY"] = "your-anthropic-key"

# OpenAI
response = completion(model="openai/gpt-4o", messages=[{"role": "user", "content": "Hello!"}])

# Anthropic  
response = completion(model="anthropic/claude-sonnet-4-20250514", messages=[{"role": "user", "content": "Hello!"}])

AI Gateway (Proxy Server)

Getting Started - E2E Tutorial - Setup virtual keys, make your first request

uv tool install 'litellm[proxy]'
litellm --model gpt-4o
import openai

client = openai.OpenAI(api_key="anything", base_url="http://0.0.0.0:4000")
response = client.chat.completions.create(
    model="gpt-4o",
    messages=[{"role": "user", "content": "Hello!"}]
)

Docs: LLM Providers

Agents - Invoke A2A Agents (Python SDK + AI Gateway)

Supported Providers - LangGraph, Vertex AI Agent Engine, Azure AI Foundry, Bedrock AgentCore, Pydantic AI

Python SDK - A2A Protocol

from litellm.a2a_protocol import A2AClient
from a2a.types import SendMessageRequest, MessageSendParams
from uuid import uuid4

client = A2AClient(base_url="http://localhost:10001")

request = SendMessageRequest(
    id=str(uuid4()),
    params=MessageSendParams(
        message={
            "role": "user",
            "parts": [{"kind": "text", "text": "Hello!"}],
            "messageId": uuid4().hex,
        }
    )
)
response = await client.send_message(request)

AI Gateway (Proxy Server)

Step 1. Add your Agent to the AI Gateway

Step 2. Call Agent via A2A SDK

from a2a.client import A2ACardResolver, A2AClient
from a2a.types import MessageSendParams, SendMessageRequest
from uuid import uuid4
import httpx

base_url = "http://localhost:4000/a2a/my-agent"  # LiteLLM proxy + agent name
headers = {"Authorization": "Bearer sk-1234"}    # LiteLLM Virtual Key

async with httpx.AsyncClient(headers=headers) as httpx_client:
    resolver = A2ACardResolver(httpx_client=httpx_client, base_url=base_url)
    agent_card = await resolver.get_agent_card()
    client = A2AClient(httpx_client=httpx_client, agent_card=agent_card)

    request = SendMessageRequest(
        id=str(uuid4()),
        params=MessageSendParams(
            message={
                "role": "user",
                "parts": [{"kind": "text", "text": "Hello!"}],
                "messageId": uuid4().hex,
            }
        )
    )
    response = await client.send_message(request)

Docs: A2A Agent Gateway

MCP Tools - Connect MCP servers to any LLM (Python SDK + AI Gateway)

Python SDK - MCP Bridge

from mcp import ClientSession, StdioServerParameters
from mcp.client.stdio import stdio_client
from litellm import experimental_mcp_client
import litellm

server_params = StdioServerParameters(command="python", args=["mcp_server.py"])

async with stdio_client(server_params) as (read, write):
    async with ClientSession(read, write) as session:
        await session.initialize()

        # Load MCP tools in OpenAI format
        tools = await experimental_mcp_client.load_mcp_tools(session=session, format="openai")

        # Use with any LiteLLM model
        response = await litellm.acompletion(
            model="gpt-4o",
            messages=[{"role": "user", "content": "What's 3 + 5?"}],
            tools=tools
        )

AI Gateway - MCP Gateway

Step 1. Add your MCP Server to the AI Gateway

Step 2. Call MCP tools via /chat/completions

curl -X POST 'http://0.0.0.0:4000/v1/chat/completions' \
  -H 'Authorization: Bearer sk-1234' \
  -H 'Content-Type: application/json' \
  -d '{
    "model": "gpt-4o",
    "messages": [{"role": "user", "content": "Summarize the latest open PR"}],
    "tools": [{
      "type": "mcp",
      "server_url": "litellm_proxy/mcp/github",
      "server_label": "github_mcp",
      "require_approval": "never"
    }]
  }'

Use with Cursor IDE

{
  "mcpServers": {
    "LiteLLM": {
      "url": "http://localhost:4000/mcp/",
      "headers": {
        "x-litellm-api-key": "Bearer sk-1234"
      }
    }
  }
}

Docs: MCP Gateway

Supported Providers (Website Supported Models | Docs)

Provider /chat/completions /messages /responses /embeddings /image/generations /audio/transcriptions /audio/speech /moderations /batches /rerank
Abliteration (abliteration)
AI/ML API (aiml)
AI21 (ai21)
AI21 Chat (ai21_chat)
Aleph Alpha
Amazon Nova
Anthropic (anthropic)
Anthropic Text (anthropic_text)
Anyscale
AssemblyAI (assemblyai)
Auto Router (auto_router)
AWS - Bedrock (bedrock)
AWS - Sagemaker (sagemaker)
Azure (azure)
Azure AI (azure_ai)
Azure Text (azure_text)
Baseten (baseten)
Bytez (bytez)
Cerebras (cerebras)
Clarifai (clarifai)
Cloudflare AI Workers (cloudflare)
Codestral (codestral)
Cohere (cohere)
Cohere Chat (cohere_chat)
CometAPI (cometapi)
CompactifAI (compactifai)
Custom (custom)
Custom OpenAI (custom_openai)
Dashscope (dashscope)
Databricks (databricks)
DataRobot (datarobot)
Deepgram (deepgram)
DeepInfra (deepinfra)
Deepseek (deepseek)
ElevenLabs (elevenlabs)
Empower (empower)
Fal AI (fal_ai)
Featherless AI (featherless_ai)
Fireworks AI (fireworks_ai)
FriendliAI (friendliai)
Galadriel (galadriel)
GitHub Copilot (github_copilot)
GitHub Models (github)
Google - PaLM
Google - Vertex AI (vertex_ai)
Google AI Studio - Gemini (gemini)
GradientAI (gradient_ai)
Groq AI (groq)
Heroku (heroku)
Hosted VLLM (hosted_vllm)
Huggingface (huggingface)
Hyperbolic (hyperbolic)
IBM - Watsonx.ai (watsonx)
Infinity (infinity)
Jina AI (jina_ai)
Lambda AI (lambda_ai)
Lemonade (lemonade)
LiteLLM Proxy (litellm_proxy)
Llamafile (llamafile)
LM Studio (lm_studio)
Maritalk (maritalk)
Meta - Llama API (meta_llama)
Mistral AI API (mistral)
Moonshot (moonshot)
Morph (morph)
Nebius AI Studio (nebius)
NLP Cloud (nlp_cloud)
Novita AI (novita)
Nscale (nscale)
Nvidia NIM (nvidia_nim)
OCI (oci)
Ollama (ollama)
Ollama Chat (ollama_chat)
Oobabooga (oobabooga)
OpenAI (openai)
OpenAI-like (openai_like)
OpenRouter (openrouter)
OVHCloud AI Endpoints (ovhcloud)
Perplexity AI (perplexity)
Petals (petals)
Predibase (predibase)
Recraft (recraft)
Replicate (replicate)
Sagemaker Chat (sagemaker_chat)
Sambanova (sambanova)
Snowflake (snowflake)
Text Completion Codestral (text-completion-codestral)
Text Completion OpenAI (text-completion-openai)
Together AI (together_ai)
Topaz (topaz)
Triton (triton)
V0 (v0)
Vercel AI Gateway (vercel_ai_gateway)
VLLM (vllm)
Volcengine (volcengine)
Voyage AI (voyage)
WandB Inference (wandb)
Watsonx Text (watsonx_text)
xAI (xai)
Xinference (xinference)

Read the Docs


Get Started

You can use LiteLLM through either the Proxy Server or Python SDK. Both give you a unified interface to access multiple LLMs (100+ LLMs). Choose the option that best fits your needs:

LiteLLM AI Gateway LiteLLM Python SDK
Use Case Central service (LLM Gateway) to access multiple LLMs Use LiteLLM directly in your Python code
Who Uses It? Gen AI Enablement / ML Platform Teams Developers building LLM projects
Key Features Centralized API gateway with authentication and authorization, multi-tenant cost tracking and spend management per project/user, per-project customization (logging, guardrails, caching), virtual keys for secure access control, admin dashboard UI for monitoring and management Direct Python library integration in your codebase, Router with retry/fallback logic across multiple deployments (e.g. Azure/OpenAI) - Router, application-level load balancing and cost tracking, exception handling with OpenAI-compatible errors, observability callbacks (Lunary, MLflow, Langfuse, etc.)

Stable Release: Use docker images with the -stable tag. These have undergone 12 hour load tests, before being published. More information about the release cycle here

Support for more providers. Missing a provider or LLM Platform, raise a feature request.

Run in Developer Mode

Services

  1. Setup .env file in root
  2. Run dependant services docker-compose up db prometheus

Backend

  1. (In root) create virtual environment python -m venv .venv
  2. Activate virtual environment source .venv/bin/activate
  3. Install dependencies uv sync --all-extras --group proxy-dev
  4. uv run prisma generate
  5. prisma generate
  6. Start proxy backend python litellm/proxy/proxy_cli.py

Frontend

  1. Navigate to ui/litellm-dashboard
  2. Install dependencies npm install
  3. Run npm run dev to start the dashboard

Verify Docker Image Signatures

All LiteLLM Docker images published to GHCR are signed with cosign. Every release is signed with the same key introduced in commit 0112e53.

Verify using the pinned commit hash (recommended):

A commit hash is cryptographically immutable, so this is the strongest way to ensure you are using the original signing key:

cosign verify \
  --key https://raw.githubusercontent.com/BerriAI/litellm/0112e53046018d726492c814b3644b7d376029d0/cosign.pub \
  ghcr.io/berriai/litellm:<release-tag>

Verify using a release tag (convenience):

Tags are protected in this repository and resolve to the same key. This option is easier to read but relies on tag protection rules:

cosign verify \
  --key https://raw.githubusercontent.com/BerriAI/litellm/<release-tag>/cosign.pub \
  ghcr.io/berriai/litellm:<release-tag>

Replace <release-tag> with the version you are deploying (e.g. v1.83.0-stable).


Enterprise

For companies that need better security, user management and professional support

Get an Enterprise License Talk to founders

This covers:

  • Features under the LiteLLM Commercial License:
  • Feature Prioritization
  • Custom Integrations
  • Professional Support - Dedicated discord + slack
  • Custom SLAs
  • Secure access with Single Sign-On

Contributing

We welcome contributions to LiteLLM! Whether you're fixing bugs, adding features, or improving documentation, we appreciate your help.

Quick Start for Contributors

This requires uv to be installed.

git clone https://github.com/BerriAI/litellm.git
cd litellm
make install-dev    # Install development dependencies
make format         # Format your code
make lint           # Run all linting checks
make test-unit      # Run unit tests
make format-check   # Check formatting only

For detailed contributing guidelines, see CONTRIBUTING.md.

📖 Contributing to documentation? The LiteLLM docs have moved to a separate repository: BerriAI/litellm-docs. Please open doc PRs there. Docs are served at docs.litellm.ai.

Code Quality / Linting

LiteLLM follows the Google Python Style Guide.

Our automated checks include:

  • Black for code formatting
  • Ruff for linting and code quality
  • MyPy for type checking
  • Circular import detection
  • Import safety checks

All these checks must pass before your PR can be merged.

Support / talk with founders

Contributors

S
Description
Python SDK, Proxy Server (AI Gateway) to call 100+ LLM APIs in OpenAI (or native) format, with cost tracking, guardrails, loadbalancing and logging. [Bedrock, Azure, OpenAI, VertexAI, Cohere, Anthropic, Sagemaker, HuggingFace, VLLM, NVIDIA NIM]
Readme MIT 1.1 GiB
Languages
Python 81%
TypeScript 12.2%
JavaScript 5.9%
HTML 0.5%
HCL 0.2%