prefecthq--fastmcp/docs/servers/auth/multi-auth.mdx

---
title: Multiple Auth Sources
sidebarTitle: Multiple Auth Sources
description: Accept tokens from multiple authentication sources with a single server.
icon: layer-group
---

import { VersionBadge } from "/snippets/version-badge.mdx"

<VersionBadge version="3.1.0" />

Production servers often need to accept tokens from multiple authentication sources. An interactive application might authenticate through an OAuth proxy, while a backend service sends machine-to-machine JWT tokens directly. `MultiAuth` composes these sources into a single `auth` provider so every valid token is accepted regardless of where it was issued.

## Understanding MultiAuth

`MultiAuth` wraps an optional auth server (like `OAuthProxy`) together with one or more token verifiers (like `JWTVerifier`). When a request arrives with a bearer token, `MultiAuth` tries each source in order and accepts the first successful verification.

The auth server, if provided, is tried first. It owns all OAuth routes and metadata — the verifiers contribute only token verification logic. This keeps the MCP discovery surface clean: one set of routes, one set of metadata, multiple verification paths.

```python
from fastmcp import FastMCP
from fastmcp.server.auth import MultiAuth, OAuthProxy
from fastmcp.server.auth.providers.jwt import JWTVerifier

auth = MultiAuth(
    server=OAuthProxy(
        issuer_url="https://login.example.com/...",
        client_id="my-app",
        client_secret="secret",
        base_url="https://my-server.com",
    ),
    verifiers=[
        JWTVerifier(
            jwks_uri="https://internal-issuer.example.com/.well-known/jwks.json",
            issuer="https://internal-issuer.example.com",
            audience="my-mcp-server",
        ),
    ],
)

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

Interactive MCP clients authenticate through the OAuth proxy as usual. Backend services skip OAuth entirely and send a JWT signed by the internal issuer. Both paths are validated, and the first match wins.

## Verification Order

`MultiAuth` checks sources in a deterministic order:

1. **Server** (if provided) — the full auth provider's `verify_token` runs first
2. **Verifiers** — each `TokenVerifier` is tried in list order

The first source that returns a valid `AccessToken` wins. If every source returns `None`, the request receives a 401 response.

This ordering means the server acts as the "primary" authentication path, with verifiers as fallbacks for tokens the server doesn't recognize.

## Verifiers Only

You don't always need a full OAuth server. If your server only needs to accept tokens from multiple issuers, pass verifiers without a server:

```python
from fastmcp import FastMCP
from fastmcp.server.auth import MultiAuth
from fastmcp.server.auth.providers.jwt import JWTVerifier, StaticTokenVerifier

auth = MultiAuth(
    verifiers=[
        JWTVerifier(
            jwks_uri="https://issuer-a.example.com/.well-known/jwks.json",
            issuer="https://issuer-a.example.com",
            audience="my-server",
        ),
        JWTVerifier(
            jwks_uri="https://issuer-b.example.com/.well-known/jwks.json",
            issuer="https://issuer-b.example.com",
            audience="my-server",
        ),
    ],
)

mcp = FastMCP("Multi-Issuer Server", auth=auth)
```

Without a server, no OAuth routes or metadata are served. This is appropriate for internal systems where clients already know how to obtain tokens.

## API Reference

### MultiAuth

| Parameter | Type | Description |
| --- | --- | --- |
| `server` | `AuthProvider \| None` | Optional auth provider that owns routes and OAuth metadata. Also tried first for token verification. |
| `verifiers` | `list[TokenVerifier] \| TokenVerifier` | One or more token verifiers tried after the server. |
| `base_url` | `str \| None` | Override the base URL. Defaults to the server's `base_url`. |
| `required_scopes` | `list[str] \| None` | Override required scopes. Defaults to the server's scopes. |