Set up the LLM auth proxy

Deploy an Envoy-based auth proxy that validates LangSmith-signed JWTs and routes LLM requests to your upstream provider or gateway.

The LLM auth proxy lets your organization enforce its own authentication flows for all model invocations from LangSmith so that provider credentials are never exposed to end users and every request is traceable back to a specific actor.

The LLM auth proxy is an Envoy-based component that runs in your environment and sits between LangSmith and your upstream LLM provider or gateway (such as OpenAI, Anthropic, or an internal LLM gateway like LiteLLM). LangSmith signs every request with a short-lived JWT (JSON Web Token). The proxy validates the JWT, optionally injects provider credentials or transforms request and response bodies, then forwards the request upstream. It is available to both SaaS and self-hosted LangSmith customers.

The LLM auth proxy requires a LangSmith Enterprise plan. For more details, refer to Pricing or contact our sales team.

Use the LLM auth proxy when you need to:

• Authenticate Playground or LLM-as-judge evaluation requests against your own provider gateway.
• Inject provider-specific API keys or auth headers without exposing them to end users.
• Transform request or response bodies (for example, converting between OpenAI format and a custom gateway format).

How it works

Each request from LangSmith passes through the following steps in the proxy:

1. Validate the JWT (signature, issuer, audience)
2. Call your ext_authz service, which receives the validated JWT and returns the provider credentials to inject as headers
3. Optionally call your ext_proc transformer, which can rewrite request and response bodies (for example, converting between OpenAI format and a custom gateway format)
4. Forward the request with custom headers (static or dynamic) to the upstream provider

Both the ext_authz service and the transformer are customer-deployed components that run alongside the proxy in your environment. Either or both can be enabled depending on your use case.

Prerequisites

• LangSmith Enterprise plan (SaaS or self-hosted on version 0.13.33+)
• Kubernetes cluster with Helm 3
• Envoy v1.37 or later (the Helm chart defaults to envoyproxy/envoy:v1.37-latest)
• The URL of your upstream LLM provider or gateway (the destination the proxy will forward requests to)

The auth proxy currently supports the Playground, Evals, Fleet, Polly, and Insights features. Playground and Evals are available in v0.13.33+. Polly and Insights are available in v0.13.39+.

1. Configure JWT signing (self-hosted LangSmith only)

Skip this step for LangSmith SaaS. JWT signing is already configured.

Generate an Ed25519 key pair using step CLI (or an internal process if you prefer). Ed25519 is the signing algorithm LangSmith uses to sign JWTs. The private key signs each request; the auth proxy verifies the signature using only the public key.

TMPDIR_KEYS="$(mktemp -d)"
step crypto keypair "$TMPDIR_KEYS/pub.pem" "$TMPDIR_KEYS/priv.pem" \
  --kty OKP --crv Ed25519 --no-password --insecure
PRIV_JWK=$(step crypto key format --jwk --no-password --insecure < "$TMPDIR_KEYS/priv.pem")
SIGNING_JWKS=$(echo "$PRIV_JWK" | jq -c '{keys: [. + {use: "sig", alg: "EdDSA"}]}')
echo "$SIGNING_JWKS"

Store the JWKS in a Kubernetes secret:

kubectl create secret generic langsmith-signing-jwks \
  --namespace <namespace> \
  --from-literal=LANGSMITH_SIGNING_JWKS="$SIGNING_JWKS"

A JWKS (JSON Web Key Set) is a standard JSON format for publishing cryptographic keys. LANGSMITH_SIGNING_JWKS contains the Ed25519 private key and is stored as a Kubernetes secret. It is never exposed. LangSmith automatically extracts the corresponding public key and serves it at /.well-known/jwks.json. The auth proxy fetches this public endpoint to verify JWT signatures without ever needing the private key.

Reference the secret in your LangSmith values.yaml:

platformBackend:
  deployment:
    extraEnv:
      - name: LLM_AUTH_PROXY_ISSUER
        value: "langsmith"        # must match jwtIssuer in the auth proxy chart
      - secretRef:
          name: langsmith-signing-jwks

LLM_AUTH_PROXY_ISSUER sets the iss claim in signed JWTs. Use langsmith to match the SaaS default, or a custom identifier like langsmith:self-hosted:<short_identifier> to distinguish your installation. The value must match jwtIssuer in the auth proxy chart in Step 4).

2. Enable LLM Auth Proxy for your organization

Self-hosted

Option A: Enable for a specific organization:

In the LangSmith UI, navigate to the Settings page, copy the organization ID at the top left next to Organizations.

Run the following against your LangSmith PostgreSQL database:

UPDATE organizations
SET config = config || '{"can_use_llm_auth_proxy": true}'
WHERE id = '<organization_id>';

Option B: Enable for all organizations in an installation:

Add the following to commonEnv in your LangSmith values.yaml:

commonEnv:
  DEFAULT_ORG_FEATURE_CAN_USE_LLM_AUTH_PROXY: "true"

This setting has no effect on Personal organizations.

SaaS

Contact LangChain support to enable LLM Auth Proxy for your organization.

3. Configure organization settings in LangSmith

In the LangSmith UI, navigate to Settings > General, configure the following:

1. JWT audience: the aud claim value the proxy will validate (for example, example-audience). This must match jwtAudiences in the auth proxy chart in Step 4.

2. Enable LLM auth proxy: toggle on for your organization.

3. Allowed URLs: control which destination URLs the proxy is permitted to forward JWTs to. This prevents credential forwarding to unintended hosts. Choose one of three options:

   • Allow all (default): permits JWT forwarding to any upstream URL. Equivalent to no restriction.
   • Block all: blocks JWT forwarding to all URLs.
   • Custom: specify an explicit list of allowed URL patterns. Empty strings and bare * are not accepted. The control is disabled when the LLM auth proxy toggle is off.
   

4. Install the auth proxy Helm chart

Add the LangChain Helm repository:

helm repo add langchain https://langchain-ai.github.io/helm/
helm repo update

Create a values.yaml with the upstream URL and JWT validation settings. There are two options for JWKS configuration:

• jwksUri (recommended): Point to your LangSmith instance’s /.well-known/jwks.json endpoint. Envoy fetches and caches the public keys automatically, supporting seamless key rotation.
• jwksJson (inline): Paste the JWKS JSON directly into values.yaml. Use this for testing or air-gapped environments where the auth proxy has no outbound network access to LangSmith. Requires a chart update to rotate keys. Include only the public key components; omit the d field (the private key).

If both are set, jwksUri takes precedence.

authProxy:
  upstream: "https://gateway.example.com"
  jwtIssuer: "langsmith" # must match LLM_AUTH_PROXY_ISSUER in LangSmith values.yaml
  jwtAudiences:
    - "example-audience" # must match the org setting in LangSmith

  # Option A: remote JWKS (recommended for production)
  # Envoy fetches and caches public keys from LangSmith's /.well-known/jwks.json.
  jwksUri: "https://langsmith.example.com/.well-known/jwks.json"       # self-hosted
  # jwksUri: "https://api.smith.langchain.com/.well-known/jwks.json"   # SaaS
  jwksCacheDurationSeconds: 300

  # Option B: inline JWKS (testing or air-gapped environments only)
  # Omit the "d" field (private key); include public key components only.
  # jwksJson: '{"keys": [{"kty": "OKP", "crv": "Ed25519", "x": "<base64url-public-key>", "use": "sig", "alg": "EdDSA"}]}'

Install the chart:

helm install langsmith-auth-proxy langchain/langsmith-auth-proxy \
  --namespace <your-namespace> \
  -f values.yaml

Write an ext_authz service

Use ext_authz when you need to add, remove, or edit authorization headers, for example, to inject a provider API key based on the identity in the JWT. Your service receives the validated JWT and optionally the request body, and returns the headers to inject upstream. This uses Envoy’s HTTP ext_authz filter (not gRPC).

Enable it in values.yaml:

authProxy:
  extAuthz:
    enabled: true
    serviceUrl: "http://my-auth-service:8080"
    timeout: "10s"

How it works

Before forwarding each request, Envoy calls your service at <serviceUrl>/check<original_path> using the same HTTP method as the original request. Your service receives the validated JWT in the x-langsmith-llm-auth header.

Your service returns a plain HTTP response:

• 2xx: allow the request. Any headers matching allowedUpstreamHeaders patterns (default: authorization and x-*) are injected into the upstream request. To strip the JWT before forwarding, include x-envoy-auth-headers-to-remove: x-langsmith-llm-auth in your response.
• Non-2xx: deny the request. The status code and any headers matching allowedClientHeaders patterns (default: www-authenticate and x-*) are returned to the client.

Deployment options

Your ext_authz service can run in two ways:

• Sidecar: run the service in the same pod as the proxy. Add the container under authProxy.deployment.sidecars and any required volumes under authProxy.deployment.volumes in values.yaml. Use a localhost URL, for example http://localhost:10002.
• Separate deployment: deploy the service independently and point extAuthz.serviceUrl at it. Use the in-cluster DNS name, for example http://my-auth-service.my-namespace.svc.cluster.local:8080, or an external HTTPS URL if the service has its own ingress.

Sample deployment

The example below is a minimal Python ext_authz service that performs an OAuth2 client credentials token exchange. On each request, it returns a cached Authorization header with a fresh access token, refreshing it from the configured token endpoint before it expires. See e2e/oauth/ in the chart repository for the full example.

ext-authz-oauth.py

"""ext_authz service that performs an OAuth2 client-credentials token exchange.

Runs as a sidecar (or standalone service) alongside the main auth-proxy component.
On each ext_authz check request it returns a cached OAuth access token,
refreshing it from the configured token endpoint when expired.

Environment variables:
  OAUTH_TOKEN_URL    – Token endpoint (e.g. https://login.example.com/oauth/token)
  OAUTH_CLIENT_ID    – Client ID for the credentials grant
  OAUTH_CLIENT_SECRET– Client secret for the credentials grant
  OAUTH_SCOPE        – (optional) Space-separated scopes to request
  LISTEN_PORT        – (optional) Port to listen on, default 10002
"""

from http.server import HTTPServer, BaseHTTPRequestHandler
import json
import os
import sys
import threading
import time
import urllib.request
import urllib.parse

# ---------------------------------------------------------------------------
# Configuration
# ---------------------------------------------------------------------------
TOKEN_URL = os.environ["OAUTH_TOKEN_URL"]
CLIENT_ID = os.environ["OAUTH_CLIENT_ID"]
CLIENT_SECRET = os.environ["OAUTH_CLIENT_SECRET"]
SCOPE = os.environ.get("OAUTH_SCOPE", "")
LISTEN_PORT = int(os.environ.get("LISTEN_PORT", "10002"))

# Refresh the token this many seconds before it actually expires.
EXPIRY_BUFFER_SECONDS = 30

# ---------------------------------------------------------------------------
# Token cache (thread-safe)
# ---------------------------------------------------------------------------
_lock = threading.Lock()
_cached_token: str | None = None
_token_expiry: float = 0  # epoch seconds


def _fetch_token() -> tuple[str, float]:
    """Perform a client_credentials grant and return (access_token, expiry_epoch)."""
    data = urllib.parse.urlencode({
        "grant_type": "client_credentials",
        "client_id": CLIENT_ID,
        "client_secret": CLIENT_SECRET,
        **({"scope": SCOPE} if SCOPE else {}),
    }).encode()

    req = urllib.request.Request(
        TOKEN_URL,
        data=data,
        headers={"Content-Type": "application/x-www-form-urlencoded"},
        method="POST",
    )
    with urllib.request.urlopen(req, timeout=10) as resp:
        body = json.loads(resp.read())

    access_token = body["access_token"]
    expires_in = int(body.get("expires_in", 3600))
    expiry = time.time() + expires_in - EXPIRY_BUFFER_SECONDS
    return access_token, expiry


def get_token() -> str:
    """Return a valid access token, refreshing if necessary."""
    global _cached_token, _token_expiry
    with _lock:
        if _cached_token and time.time() < _token_expiry:
            return _cached_token
    # Fetch outside the lock so other requests aren't blocked on I/O.
    token, expiry = _fetch_token()
    with _lock:
        _cached_token = token
        _token_expiry = expiry
    print(f"Refreshed OAuth token (expires in {int(expiry - time.time())}s)", flush=True)
    return token


# ---------------------------------------------------------------------------
# ext_authz HTTP handler
# ---------------------------------------------------------------------------
class Handler(BaseHTTPRequestHandler):
    def do_any(self):
        try:
            token = get_token()
        except Exception as exc:
            print(f"OAuth token fetch failed: {exc}", flush=True)
            self.send_response(500)
            self.send_header("Content-Type", "text/plain")
            self.end_headers()
            self.wfile.write(b"OAuth token exchange failed")
            return

        self.send_response(200)
        # Replace the header name as needed - this header will be forwarded to the upstream LLM provider / gateway.
        self.send_header("Authorization", f"Bearer {token}")
        self.end_headers()

    # Handle every method Envoy might send for ext_authz checks.
    do_GET = do_POST = do_PUT = do_DELETE = do_PATCH = do_HEAD = do_OPTIONS = do_any

    def log_message(self, format, *args):
        # Quieter logs — only print errors.
        pass


if __name__ == "__main__":
    server = HTTPServer(("0.0.0.0", LISTEN_PORT), Handler)
    print(f"ext-authz-oauth listening on :{LISTEN_PORT}", flush=True)
    print(f"  token_url={TOKEN_URL} client_id=<redacted>", flush=True)
    server.serve_forever()

For the full list of extAuthz parameters, see the Helm chart README.

Write an ext_proc transformer

Use ext_proc when you need to rewrite request or response bodies, for example, to convert between OpenAI format and a custom gateway format, or to inject additional fields into the request payload. This uses Envoy’s ext_proc filter.

Unlike ext_authz (HTTP), ext_proc uses a bidirectional gRPC stream. Envoy sends your transformer service one message per processing phase (request headers, request body, response headers, response body), and your service replies with mutations for each phase. Your transformer must implement the envoy.service.ext_proc.v3.ExternalProcessor gRPC service. See e2e/transformer/ in the chart repository for a sample Go implementation.

When to use ext_proc vs ext_authz

Capability	ext_authz	ext_proc
Modify request headers	Yes	Yes
Modify response headers	No	Yes
Modify request body	No	Yes
Modify response body	No	Yes
Protocol	HTTP	gRPC

Use ext_authz if you only need to inject auth headers, for example, for API keys. Use ext_proc if you need to rewrite bodies. Both can be enabled simultaneously.

Enable ext_proc in values.yaml:

authProxy:
  transformer:
    enabled: true
    serviceUrl: "grpc://my-transformer:50051"
    timeout: "10s"
    failureModeAllow: false
    processingMode:
      requestHeaderMode: "SEND"
      requestBodyMode: "BUFFERED"
      responseHeaderMode: "SKIP"
      responseBodyMode: "NONE"

Set failureModeAllow: true to allow requests through if the transformer is unavailable. The default (false) rejects the request.

Processing modes

Control which phases are sent to your transformer via processingMode. Only enable the phases you need, as disabling unused phases reduces latency.

Field	Options	Description
requestHeaderMode	SEND, SKIP, DEFAULT	Whether to forward request headers.
responseHeaderMode	SEND, SKIP, DEFAULT	Whether to forward response headers.
requestBodyMode	NONE, BUFFERED, STREAMED, BUFFERED_PARTIAL	How to send the request body.
responseBodyMode	NONE, BUFFERED, STREAMED, BUFFERED_PARTIAL	How to send the response body.
requestTrailerMode	SEND, SKIP	Whether to forward request trailers.
responseTrailerMode	SEND, SKIP	Whether to forward response trailers.

• Use BUFFERED for request body rewriting: buffers the full body before sending, simplest for JSON rewriting.
• Use STREAMED for streaming LLM response body rewriting: sends chunks as they arrive, lower latency but more complex to implement.
• Use NONE to skip a phase entirely.

When mutating the body, your ext_proc service must also update the content-length header to match the new body size via HeaderMutation. Envoy rejects responses where content-length does not match the mutated body.

Request flow

Example with ext_proc enabled for header injection and body rewriting:

curl -H "X-LangSmith-LLM-Auth: <JWT>" -d '{"model":"gpt-4",...}'
  -> Envoy(:10000)
  -> built-in Envoy JWT filter (validate sig, iss, aud)
  -> `ext_proc` filter -> transformer:50051 (gRPC)
    <- phase 1: request_headers -> mutate headers (inject Authorization)
    <- phase 2: request_body   -> mutate body (rewrite JSON) + update content-length
  -> upstream LLM provider or gateway

Sample deployment

The example below deploys a minimal Go transformer as a Kubernetes Deployment. It reads the JWT from request headers, injects an Authorization header, and rewrites the request body from OpenAI format to a custom format.

transformer-configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: transformer-source
data:
  main.go: |
    package main

    import (
        "encoding/json"
        "fmt"
        "io"
        "log"
        "net"
        "strings"

        core "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
        ext_proc "github.com/envoyproxy/go-control-plane/envoy/service/ext_proc/v3"
        "google.golang.org/grpc"
    )

    type server struct {
        ext_proc.UnimplementedExternalProcessorServer
    }

    func (s *server) Process(stream ext_proc.ExternalProcessor_ProcessServer) error {
        for {
            req, err := stream.Recv()
            if err == io.EOF {
                return nil
            }
            if err != nil {
                return err
            }

            var resp *ext_proc.ProcessingResponse
            switch v := req.Request.(type) {
            case *ext_proc.ProcessingRequest_RequestHeaders:
                resp = handleRequestHeaders(v.RequestHeaders)
            case *ext_proc.ProcessingRequest_RequestBody:
                resp = handleRequestBody(v.RequestBody)
            default:
                resp = &ext_proc.ProcessingResponse{}
            }

            if err := stream.Send(resp); err != nil {
                return err
            }
        }
    }

    func handleRequestHeaders(headers *ext_proc.HttpHeaders) *ext_proc.ProcessingResponse {
        var jwtValue string
        for _, h := range headers.Headers.Headers {
            if strings.EqualFold(h.Key, "x-langsmith-llm-auth") {
                if len(h.RawValue) > 0 {
                    jwtValue = string(h.RawValue)
                } else {
                    jwtValue = h.Value
                }
                break
            }
        }

        resp := &ext_proc.ProcessingResponse{
            Response: &ext_proc.ProcessingResponse_RequestHeaders{
                RequestHeaders: &ext_proc.HeadersResponse{},
            },
        }

        if jwtValue != "" {
            // TODO: Replace with your auth logic, e.g. exchange JWT for a
            // provider-specific token, call a secrets manager, etc.
            providerKey := "Bearer your-provider-key"

            headerResp := resp.GetRequestHeaders()
            headerResp.Response = &ext_proc.CommonResponse{
                HeaderMutation: &ext_proc.HeaderMutation{
                    SetHeaders: []*core.HeaderValueOption{
                        {
                            Header: &core.HeaderValue{
                                Key:      "Authorization",
                                RawValue: []byte(providerKey),
                            },
                        },
                    },
                },
            }
        }
        return resp
    }

    func handleRequestBody(body *ext_proc.HttpBody) *ext_proc.ProcessingResponse {
        resp := &ext_proc.ProcessingResponse{
            Response: &ext_proc.ProcessingResponse_RequestBody{
                RequestBody: &ext_proc.BodyResponse{},
            },
        }

        var original map[string]interface{}
        if err := json.Unmarshal(body.Body, &original); err != nil {
            log.Printf("Body parse failed, passing through: %v", err)
            return resp
        }

        // TODO: Replace with your transformation logic.
        // This example wraps the OpenAI-format body in a custom envelope.
        transformed := map[string]interface{}{
            "custom_model":    original["model"],
            "custom_messages": original["messages"],
            "metadata":        map[string]string{"source": "langsmith"},
        }

        newBody, err := json.Marshal(transformed)
        if err != nil {
            log.Printf("Body marshal failed, passing through: %v", err)
            return resp
        }

        // IMPORTANT: update content-length to match the new body size.
        bodyResp := resp.GetRequestBody()
        bodyResp.Response = &ext_proc.CommonResponse{
            Status: ext_proc.CommonResponse_CONTINUE_AND_REPLACE,
            HeaderMutation: &ext_proc.HeaderMutation{
                SetHeaders: []*core.HeaderValueOption{
                    {
                        Header: &core.HeaderValue{
                            Key:      "content-length",
                            RawValue: []byte(fmt.Sprintf("%d", len(newBody))),
                        },
                    },
                },
            },
            BodyMutation: &ext_proc.BodyMutation{
                Mutation: &ext_proc.BodyMutation_Body{
                    Body: newBody,
                },
            },
        }
        return resp
    }

    func main() {
        lis, err := net.Listen("tcp", ":50051")
        if err != nil {
            log.Fatalf("failed to listen: %v", err)
        }
        s := grpc.NewServer()
        ext_proc.RegisterExternalProcessorServer(s, &server{})
        log.Println("transformer listening on :50051")
        if err := s.Serve(lis); err != nil {
            log.Fatalf("failed to serve: %v", err)
        }
    }
  go.mod: |
    module transformer

    go 1.23

    require (
        github.com/envoyproxy/go-control-plane/envoy v1.32.4
        google.golang.org/grpc v1.72.1
    )

transformer-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: transformer
  labels:
    app: transformer
spec:
  replicas: 1
  selector:
    matchLabels:
      app: transformer
  template:
    metadata:
      labels:
        app: transformer
    spec:
      initContainers:
        - name: build
          image: golang:1.23
          command: ["sh", "-c"]
          args:
            - |
              cp /src/main.go /src/go.mod /build/ &&
              cd /build &&
              go mod tidy &&
              CGO_ENABLED=0 go build -o /build/transformer ./main.go
          volumeMounts:
            - name: source
              mountPath: /src
              readOnly: true
            - name: binary
              mountPath: /build
      containers:
        - name: transformer
          image: gcr.io/distroless/static-debian12:nonroot
          command: ["/app/transformer"]
          ports:
            - containerPort: 50051
          volumeMounts:
            - name: binary
              mountPath: /app
              readOnly: true
      volumes:
        - name: source
          configMap:
            name: transformer-source
        - name: binary
          emptyDir: {}
---
apiVersion: v1
kind: Service
metadata:
  name: transformer
  labels:
    app: transformer
spec:
  selector:
    app: transformer
  ports:
    - port: 50051
      targetPort: 50051
      protocol: TCP

For production, pre-build a container image instead of compiling in an init container. See e2e/transformer/Dockerfile in the Helm chart repository for an example multi-stage build.

Additional configuration

HTTP proxy

Envoy does not respect HTTP_PROXY, HTTPS_PROXY, or NO_PROXY environment variables. Configure an HTTP proxy explicitly:

authProxy:
  httpProxy:
    enabled: true
    host: "proxy.example.com"
    port: 3128
    noProxy:
      - "internal.corp"
      - ".internal.corp"

Other options

For ingress, autoscaling, resource limits, and other configuration options, see the Helm chart README.

For production reliability, set authProxy.autoscaling.hpa.minReplicas to at least 3.

Full configuration example

authProxy:
  upstream: "https://gateway.example.com"   # your LLM gateway or provider
  jwtIssuer: "langsmith"                    # must match LLM_AUTH_PROXY_ISSUER on LangSmith
  jwtAudiences:
    - "example-audience"                    # must match org setting in LangSmith

  # Option A: remote JWKS (recommended for production)
  # Envoy fetches and caches public keys from LangSmith's /.well-known/jwks.json endpoint.
  jwksUri: "https://langsmith.example.com/.well-known/jwks.json"   # self-hosted
  # jwksUri: "https://api.smith.langchain.com/.well-known/jwks.json"  # SaaS
  jwksCacheDurationSeconds: 300             # how long Envoy caches the JWKS (default 5 min)

  # Option B: inline JWKS (testing or air-gapped environments only)
  # jwksJson: '{"keys": [...]}'

  # ext_authz: header-only auth logic (include only if needed)
  # Use this to inject, remove, or modify authorization headers.
  # Your service receives an HTTP request at /check with the validated JWT
  # in the x-langsmith-llm-auth header and responds with headers to inject upstream.
  extAuthz:
    enabled: true
    serviceUrl: "http://localhost:10002"    # sidecar URL
    # serviceUrl: "http://ext-authz.<namespace>.svc.cluster.local:10002"  # separate deployment
    sendBody: false                         # set true to include request body

  # transformer: request/response body transformation (include only if needed)
  # Use this when you need to rewrite request or response bodies (e.g. OpenAI -> custom format).
  # Can be enabled alongside ext_authz.
  transformer:
    enabled: true
    serviceUrl: "grpc://transformer.<namespace>.svc.cluster.local:50051"
    timeout: "10s"
    failureModeAllow: false                 # reject if transformer is unavailable
    processingMode:
      requestHeaderMode: "SEND"             # forward request headers (read JWT, inject auth)
      responseHeaderMode: "SKIP"            # skip response headers
      requestBodyMode: "BUFFERED"           # buffer full body for JSON rewriting
      responseBodyMode: "NONE"              # skip response body
      requestTrailerMode: "SKIP"
      responseTrailerMode: "SKIP"

JWT claims reference

LangSmith signs JWTs using Ed25519 (EdDSA). Public keys are served at /.well-known/jwks.json and fetched automatically by the proxy. The auth proxy validates signatures using these public keys.

Claim	Description
iat, exp, jti, nbf	Standard JWT claims (issued-at, expiry, JWT ID, not-before)
iss	Issuer. langsmith for SaaS; set via LLM_AUTH_PROXY_ISSUER for self-hosted
aud	Audience. Matches the JWT audience in LangSmith organization settings
sub	Actor identifier (user ID, evaluator ID, assistant ID, or API key ID)
actor_type	One of: user, evaluator, agent-builder, api_key
workspace_id	Workspace ID
workspace_name	Workspace Name
organization_id	Organization ID
organization_name	Organization Name
request_id	Request correlation ID
ls_user_id	LangSmith user ID (present only when actor_type is user)

The JWT is passed to your ext_authz or transformer service in the x-langsmith-llm-auth request header.

FAQ

Does the auth proxy support corporate proxies?

Yes. Configure an HTTP proxy via the httpProxy section in values.yaml. See HTTP proxy for details.

Does the auth proxy support custom certificates?

Yes, via customCa for custom CA certificates and mtls for mutual TLS.

Can a single auth proxy route to multiple upstream LLM gateways?

No. The auth proxy has a single upstream field.

Can the auth proxy serve multiple organizations?

Yes. Multiple organizations can point to the same auth proxy instance via their model configuration in LangSmith.

Can the LangSmith to auth proxy connection use HTTP instead of HTTPS?

Yes, but only in self-hosted, and we generally recommend placing the auth proxy behind a dedicated ingress so communication uses HTTPS. To allow HTTP, add LLM_AUTH_PROXY_ACCEPT_HTTP to commonEnv and playground.deployment.extraEnv in your LangSmith values.yaml. To enable HTTP traffic to the auth proxy for Polly and Insights, set this environment variable in the respective extraEnv sections: config.polly.agent.extraEnv and config.insights.agent.extraEnv.

Helm chart reference

For the full list of configurable values, see the Helm chart README.

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