feat: add passthrough_auth option for forwarding client Authorization header (#687)

* feat: add passthrough_auth option for forwarding client Authorization header

* fix tests

* Update comment to reflect upstream forwarding

* Apply suggestions from code review

---------

Co-authored-by: Adil Hafeez <adil.hafeez@gmail.com>
Co-authored-by: Adil Hafeez <adil@katanemo.com>
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Tang Quoc Thai 2026-01-15 00:06:28 +01:00 committed by GitHub
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8 changed files with 177 additions and 26 deletions

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@ -728,6 +728,75 @@ Configure routing preferences for dynamic model selection:
- name: creative_writing
description: creative content generation, storytelling, and writing assistance
.. _passthrough_auth:
Passthrough Authentication
~~~~~~~~~~~~~~~~~~~~~~~~~~
When deploying Plano in front of LLM proxy services that manage their own API key validation (such as LiteLLM, OpenRouter, or custom gateways), you may want to forward the client's original ``Authorization`` header instead of replacing it with a configured ``access_key``.
The ``passthrough_auth`` option enables this behavior:
.. code-block:: yaml
llm_providers:
# Forward client's Authorization header to LiteLLM
- model: openai/gpt-4o-litellm
base_url: https://litellm.example.com
passthrough_auth: true
default: true
# Forward to OpenRouter
- model: openai/claude-3-opus
base_url: https://openrouter.ai/api/v1
passthrough_auth: true
**How it works:**
1. Client sends a request with ``Authorization: Bearer <virtual-key>``
2. Plano preserves this header instead of replacing it with ``access_key``
3. The upstream service (e.g., LiteLLM) validates the virtual key
4. Response flows back through Plano to the client
**Use Cases:**
- **LiteLLM Integration**: Route requests to LiteLLM which manages virtual keys and rate limits
- **OpenRouter**: Forward requests to OpenRouter with per-user API keys
- **Custom API Gateways**: Integrate with internal gateways that have their own authentication
- **Multi-tenant Deployments**: Allow different clients to use their own credentials
**Important Notes:**
- When ``passthrough_auth: true`` is set, the ``access_key`` field is ignored (a warning is logged if both are configured)
- If the client doesn't provide an ``Authorization`` header, the request is forwarded without authentication (upstream will likely return 401)
- The ``base_url`` is typically required when using ``passthrough_auth``
**Configuration with LiteLLM example:**
.. code-block:: yaml
# plano_config.yaml
version: v0.3.0
listeners:
- name: llm
type: model
port: 10000
model_providers:
- model: openai/gpt-4o
base_url: https://litellm.example.com
passthrough_auth: true
default: true
.. code-block:: bash
# Client request - virtual key is forwarded to upstream
curl http://localhost:10000/v1/chat/completions \
-H "Authorization: Bearer sk-litellm-virtual-key-abc123" \
-H "Content-Type: application/json" \
-d '{"model": "gpt-4o", "messages": [{"role": "user", "content": "Hello"}]}'
Model Selection Guidelines
--------------------------

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@ -1,26 +1,22 @@
# Arch Gateway configuration version
version: v0.3.0
# External HTTP agents - API type is controlled by request path (/v1/responses, /v1/messages, /v1/chat/completions)
agents:
- id: weather_agent # Example agent for weather
- id: weather_agent # Example agent for weather
url: http://host.docker.internal:10510
- id: flight_agent # Example agent for flights
- id: flight_agent # Example agent for flights
url: http://host.docker.internal:10520
# MCP filters applied to requests/responses (e.g., input validation, query rewriting)
filters:
- id: input_guards # Example filter for input validation
- id: input_guards # Example filter for input validation
url: http://host.docker.internal:10500
# type: mcp (default)
# transport: streamable-http (default)
# tool: input_guards (default - same as filter id)
# LLM provider configurations with API keys and model routing
model_providers:
- model: openai/gpt-4o
@ -36,6 +32,12 @@ model_providers:
- model: mistral/ministral-3b-latest
access_key: $MISTRAL_API_KEY
# Example: Passthrough authentication for LiteLLM or similar proxies
# When passthrough_auth is true, client's Authorization header is forwarded
# instead of using the configured access_key
- model: openai/gpt-4o-litellm
base_url: https://litellm.example.com
passthrough_auth: true
# Model aliases - use friendly names instead of full provider model names
model_aliases:
@ -45,7 +47,6 @@ model_aliases:
smart-llm:
target: gpt-4o
# HTTP listeners - entry points for agent routing, prompt targets, and direct LLM access
listeners:
# Agent listener for routing requests to multiple agents
@ -73,7 +74,6 @@ listeners:
port: 10000
# This listener is used for prompt_targets and function calling
# Reusable service endpoints
endpoints:
app_server:
@ -83,7 +83,6 @@ endpoints:
mistral_local:
endpoint: 127.0.0.1:8001
# Prompt targets for function calling and API orchestration
prompt_targets:
- name: get_current_weather
@ -103,7 +102,6 @@ prompt_targets:
path: /weather
http_method: POST
# OpenTelemetry tracing configuration
tracing:
# Random sampling percentage (1-100)

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@ -64,6 +64,15 @@ listeners:
model: ministral-3b-latest
name: mistral/ministral-3b-latest
provider_interface: mistral
- base_url: https://litellm.example.com
cluster_name: openai_litellm.example.com
endpoint: litellm.example.com
model: gpt-4o-litellm
name: openai/gpt-4o-litellm
passthrough_auth: true
port: 443
protocol: https
provider_interface: openai
name: egress_traffic
port: 12000
timeout: 30s
@ -91,6 +100,15 @@ model_providers:
model: ministral-3b-latest
name: mistral/ministral-3b-latest
provider_interface: mistral
- base_url: https://litellm.example.com
cluster_name: openai_litellm.example.com
endpoint: litellm.example.com
model: gpt-4o-litellm
name: openai/gpt-4o-litellm
passthrough_auth: true
port: 443
protocol: https
provider_interface: openai
- internal: true
model: Arch-Function
name: arch-function