Hugging Face

KnowledgePublisher: Hugging Face

Route Hugging Face MCP traffic through Formal to control and log what AI agents do in Hugging Face:

Block tools you don’t want agents to call, such as dataset_search.
Mask sensitive data in tool results, such as emails and phone numbers in model_search responses.
Keep credentials at the Connector, so users and agents never see Hugging Face tokens.
Log every tool call with the user, the MCP client and its parameters.

0. Prepare your Connector

The Connector needs an MCP listener and a hostname with wildcard DNS and TLS. Set them up once by following Deploy the Connector. Every MCP server reuses them.

1. Add Hugging Face MCP server to your Resources

UI
Terraform
Pulumi
API

Open the Admin Catalog and click Add MCP.
Select the Hugging Face template.
Enter a DNS-label Name, such as hugging-face.
Choose the Space containing your Connector, such as default.
Configure upstream authentication as described below, then save.

If no Connector is in the selected Space, the Configuration tab shows MCP clients can’t connect directly yet. The reason reads: No Connector is in this server's Space.

Set space_id to the ID of the Space containing your Connector.

resource "formal_resource" "hugging_face" {
  name                    = "hugging-face"
  technology              = "mcp"
  hostname                = "huggingface.co"
  space_id                = "<SPACE_ID>"
  native_users_v3_enabled = true
  port                    = 443
  tags = {
    "mcp-endpoint" = "/mcp"
  }
}

resource "formal_resource_oauth_settings" "hugging_face" {
  resource_id = formal_resource.hugging_face.id
}

Set spaceId to the ID of the Space containing your Connector.

import * as formal from "@formalco/pulumi";

const resource = new formal.Resource("mcp", {
  name: "hugging-face",
  technology: "mcp",
  hostname: "huggingface.co",
  port: 443,
  spaceId: "<SPACE_ID>",
  tags: { "mcp-endpoint": "/mcp" },
  nativeUsersV3Enabled: true,
});

new formal.ResourceOauthSettings("mcpOAuth", {
  resourceId: resource.id,
});

Create a Resource with the MCP endpoint and its Space ID.

export FORMAL_API_KEY="<YOUR_API_KEY>"
RESOURCE_RESPONSE=$(curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.ResourceService/CreateResource \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @- <<JSON
  {
    "name": "hugging-face",
    "hostname": "huggingface.co",
    "port": 443,
    "technology": "mcp",
    "spaceId": "<SPACE_ID>",
    "tags": [
      {
        "key": "mcp-endpoint",
        "value": "/mcp"
      }
    ]
  }
JSON
)
RESOURCE_ID=$(printf '%s' "${RESOURCE_RESPONSE}" | jq -r '.resource.id')
curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.ResourceService/CreateResourceOAuthSettings \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @- <<JSON
  {
    "resourceId": "${RESOURCE_ID}"
  }
JSON

2. Setup Authentication

Linked Accounts (Recommended)
Shared Credentials
Pass Through

Each user links their own Hugging Face account once in the Employee Catalog, and the Connector sends that user’s token to Hugging Face.

Linked Accounts selected under How does Formal authenticate to this resource?

Under OAuth app, choose one of the two options.

1. Formal’s App (default)

Formal has a registered OAuth app with Hugging Face, so you register nothing. Users see Formal on Hugging Face’s consent screen.

2. Your OAuth App

Users see your app’s name on Hugging Face’s consent screen.

Set up your own Hugging Face OAuth app

See Hugging Face OAuth documentation and register an app.

Create an OAuth app

Open Connected Apps settings to create a new OAuth app. Enter a name for it.

Add the redirect URI

Paste Formal’s Redirect URI into the app’s redirect URIs field. It must match exactly.

Choose scopes

Select openid, profile, and read-mcp. Add read-repos, jobs, contribute-repos, or inference-api only if your tools need them.

Copy the credentials

Save the app, then copy its Client ID and Client secret. You can skip the client secret. Formal then authenticates with PKCE alone.

Enter the app in Formal

UI
Terraform
Pulumi
API

Back in the Admin Catalog, enter the Client ID and Client secret, then save. Users then link their accounts on the Hugging Face server’s page in the Employee Catalog.

Your OAuth App selected in the Admin Catalog, with the Redirect URI, Client ID and Client secret fields

Use these OAuth settings instead of the ones from step 1.

variable "hugging_face_oauth_client_secret" {
  type      = string
  sensitive = true
}

resource "formal_resource_oauth_settings" "hugging_face" {
  resource_id              = formal_resource.hugging_face.id
  upstream_oauth_mode      = "pre_registered"
  client_id                = "<YOUR_CLIENT_ID>"
  client_secret_wo         = var.hugging_face_oauth_client_secret
  client_secret_wo_version = 1
}

Use these OAuth settings instead of the ones from step 1. Store the secret with pulumi config set --secret huggingFaceOauthClientSecret.

import * as pulumi from "@pulumi/pulumi";

const config = new pulumi.Config();

new formal.ResourceOauthSettings("mcpOAuth", {
  resourceId: resource.id,
  upstreamOauthMode: "pre_registered",
  clientId: "<YOUR_CLIENT_ID>",
  clientSecret: config.requireSecret("huggingFaceOauthClientSecret"),
});

Use this call instead of the CreateResourceOAuthSettings call from step 1. The OAuth app is fixed at creation.

curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.ResourceService/CreateResourceOAuthSettings \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @- <<JSON
  {
    "resourceId": "${RESOURCE_ID}",
    "upstreamOauthMode": "pre_registered",
    "clientId": "<YOUR_CLIENT_ID>",
    "clientSecret": "<YOUR_CLIENT_SECRET>"
  }
JSON

Switching between Formal’s App and your OAuth app unlinks every account. Users must link again.

An administrator stores one Hugging Face token in Formal, and the Connector sends it on every user’s requests without showing it to them.

Shared Credentials selected under How does Formal authenticate to this resource?

Hugging Face’s MCP endpoint accepts an User Access Token as a Bearer token. Create one at huggingface.co/settings/tokens.

Open this server from the Admin Catalog.
Select Configuration, then Authentication.
Choose Shared Credentials, then select Add credential.
Enter the credential, make it the default, and select Save authentication.

See Native Users.For HTTP Bearer authentication, enter the raw token. The Connector adds the Bearer prefix.In the Terraform tab, set native_users_v3_enabled = true on the Resource and upstream_oauth_mode = "none" on its OAuth settings.

variable "mcp_shared_credential" {
  type      = string
  sensitive = true
}

resource "formal_native_user_v3" "mcp_shared_credential" {
  resource_id = formal_resource.hugging_face.id
  label       = "shared-credential"

  http_bearer {
    header = "Authorization"
    token {
      literal_wo         = var.mcp_shared_credential
      literal_wo_version = 1
    }
  }
}

resource "formal_resource_native_user_selection" "mcp_shared_credential" {
  resource_id = formal_resource.hugging_face.id
  cel         = "\"${formal_native_user_v3.mcp_shared_credential.id}\""
}

3. Route Endpoint traffic

Auth is managed at the Connector level when you use Linked Accounts or Shared Credentials, so the Endpoint needs to forward the MCP traffic to it. Laptops and VMs with the Formal Endpoint keep using https://huggingface.co/mcp, and a network rule sends that traffic to the Connector.

UI
Terraform
Pulumi
API

Go to Network Rules and create a rule named hugging-face-mcp.
Paste this expression, set the rule to Active, then save:

{
  "condition": {
    "pre_tcp": process.is_agent,
    // Every MCP server added to Formal: process.is_agent && resource.technology == "mcp"
    "pre_tls": process.is_agent && hostname == "huggingface.co",
    "post_tls": true
  },
  "outputs": {
    "forward_to_connector": true
  }
}

resource "formal_network_rule" "hugging_face_mcp" {
  name        = "hugging-face-mcp"
  description = "Forward Hugging Face MCP traffic from agents to the Connector"
  status      = "active"

  # Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
  cel_expression = <<-EOT
    {
      "condition": {
        "pre_tcp": process.is_agent,
        "pre_tls": process.is_agent && hostname == "huggingface.co",
        "post_tls": true
      },
      "outputs": {
        "forward_to_connector": true
      }
    }
  EOT
}

import * as formal from "@formalco/pulumi";

new formal.NetworkRule("huggingFaceMcp", {
  name: "hugging-face-mcp",
  description: "Forward Hugging Face MCP traffic from agents to the Connector",
  status: "active",
  // Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
  celExpression: `
    {
      "condition": {
        "pre_tcp": process.is_agent,
        "pre_tls": process.is_agent && hostname == "huggingface.co",
        "post_tls": true
      },
      "outputs": {
        "forward_to_connector": true
      }
    }
  `,
});

export FORMAL_API_KEY="<YOUR_API_KEY>"
# Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
CEL_EXPRESSION=$(cat <<'CEL'
{
  "condition": {
    "pre_tcp": process.is_agent,
    "pre_tls": process.is_agent && hostname == "huggingface.co",
    "post_tls": true
  },
  "outputs": {
    "forward_to_connector": true
  }
}
CEL
)
jq -n --arg cel "${CEL_EXPRESSION}" '{
  name: "hugging-face-mcp",
  description: "Forward Hugging Face MCP traffic from agents to the Connector",
  status: "active",
  celExpression: $cel
}' | curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.DesktopService/CreateDesktopRoutingRule \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @-

The rule matches known agents only. See Identity headers.Cloud agents such as Claude, ChatGPT and Cursor Cloud Agents don’t run the Endpoint. Point them at this server’s Connector address, https://hugging-face.<connector-hostname>/mcp. Find it in the Admin Catalog: open Hugging Face, then copy Connector address on the Configuration tab.

4. Create policies

Tools

The Admin Catalog lists these tools for Hugging Face:

Tool	Description
`model_search`	Search models on the Hugging Face Hub.
`dataset_search`	Search datasets.
`space_search`	Search Spaces.
`paper_search`	Search research papers.
`hub_repo_details`	Retrieve repository metadata.
`hf_doc_search`	Search Hugging Face documentation.

5. Check the logs

Open Logs and search for resource.name:hugging-face. Each Hugging Face tool call is one request log with the user, the MCP client and the tool. Open a log to see its tool parameters and the policies it triggered.See Logs for search syntax and filters.

Troubleshooting

The agent says Hugging Face rejected your credentials

The agent relays: hugging-face rejected your credentials. Link or re-link your hugging-face account in Formal…Cause: Hugging Face no longer accepts the linked token, for example after the user revoked access in Hugging Face.Fix: Link Hugging Face again from the Employee Catalog.With Shared Credentials, the message asks the user to contact an administrator. Replace the token in the server’s Shared Credentials.

Laptop traffic doesn't appear in Logs

Cause: The Endpoint isn’t running, or the network rule doesn’t match the client.Fix: Check the Endpoint is connected. The rule above only matches known agents. Other clients, such as a browser, reach Hugging Face directly unless the rule also matches them. See Network rules.

MCP clients can't connect directly yet

Cause: The Configuration tab lists the reason, most often No Connector is in this server's Space.Fix: Edit the server and choose the Space containing its Connector.

Getting Started

Example Use Cases

AI Governance

Configuring Formal

Integrations

Configuration

0. Prepare your Connector

1. Add Hugging Face MCP server to your Resources

2. Setup Authentication

1. Formal’s App (default)

2. Your OAuth App

3. Route Endpoint traffic

4. Create policies

Tools

5. Check the logs

Troubleshooting

Next Steps

MCP Gateway

All MCP servers

​0. Prepare your Connector

​1. Add Hugging Face MCP server to your Resources

​2. Setup Authentication

​1. Formal’s App (default)

​2. Your OAuth App

​3. Route Endpoint traffic

​4. Create policies

​Tools

​5. Check the logs

​Troubleshooting

​Next Steps

MCP Gateway

All MCP servers

0. Prepare your Connector

1. Add Hugging Face MCP server to your Resources

2. Setup Authentication

1. Formal’s App (default)

2. Your OAuth App

3. Route Endpoint traffic

4. Create policies

Tools

5. Check the logs

Troubleshooting

Next Steps