OIDC Proxy

The OIDC proxy enables FastMCP servers to authenticate with OIDC providers that don’t support Dynamic Client Registration (DCR) out of the box. This includes OAuth providers like: Auth0, Google, Azure, AWS, etc. For providers that do support DCR (like WorkOS AuthKit), use RemoteAuthProvider instead. The OIDC proxy is built upon OAuthProxy so it has all the same functionality under the covers.

Implementation

Provider Setup Requirements

Before using the OIDC proxy, you need to register your application with your OAuth provider:

Register your application in the provider’s developer console (Auth0 Applications, Google Cloud Console, Azure Portal, etc.)
Configure the redirect URI as your FastMCP server URL plus your chosen callback path:
- Default: https://your-server.com/auth/callback
- Custom: https://your-server.com/your/custom/path (if you set redirect_path)
- Development: http://localhost:8000/auth/callback
Obtain your credentials: Client ID and Client Secret

The redirect URI you configure with your provider must exactly match your FastMCP server’s URL plus the callback path. If you customize redirect_path in the OIDC proxy, update your provider’s redirect URI accordingly.

Basic Setup

Here’s how to implement the OIDC proxy with any provider:

from fastmcp import FastMCP
from fastmcp.server.auth.oidc_proxy import OIDCProxy

# Create the OIDC proxy
auth = OIDCProxy(
    # Provider's configuration URL
    config_url="https://provider.com/.well-known/openid-configuration",

    # Your registered app credentials
    client_id="your-client-id",
    client_secret="your-client-secret",

    # Your FastMCP server's public URL
    base_url="https://your-server.com",

    # Optional: customize the callback path (default is "/auth/callback")
    # redirect_path="/custom/callback",
)

mcp = FastMCP(name="My Server", auth=auth)

Configuration Parameters

OIDCProxy Parameters

str

required

URL of your OAuth provider’s OIDC configuration

str

required

Client ID from your registered OAuth application

str | None

Client secret from your registered OAuth application. Optional for PKCE public clients. When omitted, jwt_signing_key must be provided.

AnyHttpUrl | str

required

Public URL of your FastMCP server (e.g., https://your-server.com)

AnyHttpUrl | str | None

Optional public base URL for the protected resource metadata and token audience.Use this when your OAuth callbacks and operational endpoints need to live under one public URL, but the protected MCP resource should be advertised under another. FastMCP will still append the MCP mount path (for example, /mcp) to this base URL.

bool | None

Strict flag for configuration validation. When True, requires all OIDC mandatory fields.

str | None

Audience parameter for OIDC providers that require it (e.g., Auth0). This is typically your API identifier.

int | None

default:"10"

HTTP request timeout in seconds for fetching OIDC configuration

TokenVerifier | None

Custom token verifier for validating tokens. When provided, FastMCP uses your custom verifier instead of creating a default JWTVerifier.Cannot be used with algorithm or required_scopes parameters - configure these on your verifier instead. The verifier’s required_scopes are automatically loaded and advertised.

str | None

JWT algorithm to use for token verification (e.g., “RS256”). If not specified, uses the provider’s default. Only used when token_verifier is not provided.

list[str] | None

List of OAuth scopes for token validation. These are automatically included in authorization requests. Only used when token_verifier is not provided.

str

default:"/auth/callback"

Path for OAuth callbacks. Must match the redirect URI configured in your OAuth application

list[str] | None

List of allowed redirect URI patterns for MCP clients. Patterns support wildcards (e.g., "http://localhost:*", "https://*.example.com/*").

None (default): DCR clients use registered redirect URIs, with loopback ports allowed to vary for MCP compatibility. Unsafe browser schemes such as javascript:, data:, file:, and vbscript: are rejected.
Empty list []: No redirect URIs allowed
Custom list: Only matching patterns allowed

These patterns apply to MCP client loopback redirects. Configure the upstream OAuth app redirect URI separately with redirect_path.

list[str] | None

The complete set of scopes clients are allowed to request — the full set of available scopes (a superset of required_scopes). These are advertised to clients through the /.well-known endpoints (as scopes_supported) and enforced at Dynamic Client Registration: a client registering with a scope outside this set is rejected. Defaults to required_scopes from your token verifier if not specified.

str | None

Token endpoint authentication method for the upstream OAuth server. Controls how the proxy authenticates when exchanging authorization codes and refresh tokens with the upstream provider.

"client_secret_basic": Send credentials in Authorization header (most common)
"client_secret_post": Send credentials in request body (required by some providers)
"none": No authentication (for public clients)
None (default): Uses authlib’s default (typically "client_secret_basic")

Set this if your provider requires a specific authentication method and the default doesn’t work.

str | bytes | None

Secret used to sign FastMCP JWT tokens issued to clients. bytes are used as-is, with no stretching, so supply at least 32 bytes of high-entropy key material. With the default file-backed client storage, the bytes must also decode as UTF-8; use secrets.token_urlsafe(32).encode() instead of raw secrets.token_bytes(), or configure client_storage explicitly. A string is stretched into a 32-byte key with PBKDF2 (1,000,000 iterations), since a supplied string may be low-entropy.Default behavior (None): The key is deterministically derived from client_secret using HKDF, on every platform. Because the derivation is deterministic, the same key is produced across restarts as long as client_secret doesn’t change, so tokens remain valid without any extra configuration. This convenience makes it only suitable for development and local testing.For production: Provide an explicit jwt_signing_key (e.g., from an environment variable) rather than relying on the auto-derived key.

AsyncKeyValue | None

Storage backend for persisting OAuth client registrations and upstream tokens.Default behavior: Encrypted disk store in your platform’s data directory (derived from platformdirs), on every platform including Linux. The encryption key is itself derived from jwt_signing_key.By default, clients are automatically persisted to encrypted disk storage, allowing them to survive server restarts as long as the filesystem remains accessible. This means MCP clients only need to register once and can reconnect seamlessly.For production deployments with multiple servers or cloud deployments, use a network-accessible storage backend rather than local disk storage. Wrap your storage in FernetEncryptionWrapper to encrypt sensitive OAuth tokens at rest. See Storage Backends for available options.Testing with in-memory storage (unencrypted):

from key_value.aio.stores.memory import MemoryStore

# Use in-memory storage for testing (clients lost on restart)
auth = OIDCProxy(..., client_storage=MemoryStore())

Production with encrypted Redis storage:

from key_value.aio.stores.redis import RedisStore
from key_value.aio.wrappers.encryption import FernetEncryptionWrapper
from cryptography.fernet import Fernet
import os

auth = OIDCProxy(
    ...,
    jwt_signing_key=os.environ["JWT_SIGNING_KEY"],
    client_storage=FernetEncryptionWrapper(
        key_value=RedisStore(host="redis.example.com", port=6379),
        fernet=Fernet(os.environ["STORAGE_ENCRYPTION_KEY"])
    )
)

Consent screen behavior for authorization requests. Accepts True (default; always prompt — strongest protection), "remember" (silent consent on return visits via signed cookie, gated by Sec-Fetch-Site to block AS-in-the-middle attacks), "external" (consent handled by upstream IdP or custom page), or False (disable entirely; local/testing only). See the OAuthProxy documentation for full details on each mode and the security trade-offs.

Content Security Policy for the consent page.

None (default): Uses the built-in CSP policy with appropriate directives for form submission
Empty string "": Disables CSP entirely (no meta tag rendered)
Custom string: Uses the provided value as the CSP policy

This is useful for organizations that have their own CSP policies and need to override or disable FastMCP’s built-in CSP directives.

Using Built-in Providers

FastMCP includes pre-configured OIDC providers for common services:

from fastmcp.server.auth.providers.auth0 import Auth0Provider

auth = Auth0Provider(
    config_url="https://.../.well-known/openid-configuration",
    client_id="your-auth0-client-id",
    client_secret="your-auth0-client-secret",
    audience="https://...",
    base_url="https://localhost:8000"
)

mcp = FastMCP(name="My Server", auth=auth)

Available providers include Auth0Provider at present.

Scope Configuration

OAuth scopes are configured with required_scopes to automatically request the permissions your application needs. Dynamic clients created by the proxy will automatically include these scopes in their authorization requests.

CIMD Support

The OIDC proxy inherits full CIMD (Client ID Metadata Document) support from OAuthProxy. Clients can use HTTPS URLs as their client_id instead of registering dynamically, and the proxy will fetch and validate their metadata document. See the OAuth Proxy CIMD documentation for complete details on how CIMD works, including private key JWT authentication and security considerations. The CIMD-related parameters available on OIDCProxy are:

CIMD Parameters

bool

default:"True"

Whether to accept CIMD URLs as client identifiers.

Production Configuration

For production deployments, load sensitive credentials from environment variables:

import os
from fastmcp import FastMCP
from fastmcp.server.auth.providers.auth0 import Auth0Provider

# Load secrets from environment variables
auth = Auth0Provider(
    config_url=os.environ.get("AUTH0_CONFIG_URL"),
    client_id=os.environ.get("AUTH0_CLIENT_ID"),
    client_secret=os.environ.get("AUTH0_CLIENT_SECRET"),
    audience=os.environ.get("AUTH0_AUDIENCE"),
    base_url=os.environ.get("BASE_URL", "https://localhost:8000")
)

mcp = FastMCP(name="My Server", auth=auth)

@mcp.tool
def protected_tool(data: str) -> str:
    """This tool is now protected by OAuth."""
    return f"Processed: {data}"

if __name__ == "__main__":
    mcp.run(transport="http", port=8000)

This keeps secrets out of your codebase while maintaining explicit configuration.

Get Started

Servers

Apps

Clients

Integrations

More

Implementation

Provider Setup Requirements

Basic Setup

Configuration Parameters

OIDCProxy Parameters

Using Built-in Providers

Scope Configuration

CIMD Support

CIMD Parameters

Production Configuration

​Implementation

​Provider Setup Requirements

​Basic Setup

​Configuration Parameters

OIDCProxy Parameters

​Using Built-in Providers

​Scope Configuration

​CIMD Support

CIMD Parameters

​Production Configuration

Implementation

Provider Setup Requirements

Basic Setup

Configuration Parameters

Using Built-in Providers

Scope Configuration

CIMD Support

Production Configuration