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Use MCP flows with MSAL Node

When building Model Context Protocol (MCP) applications, you can configure MSAL Node to enforce resource-scoped token acquisition and caching. When MCP mode is enabled, MSAL requires every token request to include a resource parameter and caches access tokens keyed by that resource.

Note

MCP flows are available for public client applications only.

Prerequisites

Enable MCP mode

Set isMcp: true in the auth configuration when creating your PublicClientApplication:

const config = {
    auth: {
        clientId: "your-client-id",
        authority: "https://login.microsoftonline.com/common",
        isMcp: true,
    },
};

const pca = new msal.PublicClientApplication(config);

Include the resource parameter

When isMcp is true, every token request must include a resource parameter. Omitting it throws a resource_parameter_required error.

const tokenRequest = {
    scopes: ["User.Read"],
    redirectUri: "http://localhost:3000/redirect",
    resource: "https://example.microsoft.com",
    code: authorizationCode,
};

const response = await pca.acquireTokenByCode(tokenRequest);

Important

Set the resource parameter directly on the request object. Do not pass it via extraQueryParameters at the same time as the resource property — doing so throws a misplaced_resource_parameter error.

The following example shows the correct and incorrect ways to set the resource parameter:

// Correct — resource on the request object
const request = {
    scopes: ["User.Read"],
    resource: "https://example.microsoft.com",
};

// Wrong — resource in both locations
const request = {
    scopes: ["User.Read"],
    resource: "https://example.microsoft.com",
    extraQueryParameters: { resource: "https://example.microsoft.com" },
};

Resource-scoped caching

When isMcp is enabled, access tokens are cached with their associated resource. This affects silent token acquisition:

  • Cache hit: If a cached access token exists for the same scopes and resource, it's returned from cache.
  • Cache miss: If the requested resource doesn't match any cached token, MSAL falls back to the network to acquire a new token for the requested resource.
const msalTokenCache = pca.getTokenCache();
const accounts = await msalTokenCache.getAllAccounts();

// First request — acquires token from network
const token1 = await pca.acquireTokenSilent({
    scopes: ["User.Read"],
    resource: "https://resource-a.microsoft.com",
    account: accounts[0],
});

// Same resource — returns cached token
const token2 = await pca.acquireTokenSilent({
    scopes: ["User.Read"],
    resource: "https://resource-a.microsoft.com",
    account: accounts[0],
});

// Different resource — falls back to network
const token3 = await pca.acquireTokenSilent({
    scopes: ["User.Read"],
    resource: "https://resource-b.microsoft.com",
    account: accounts[0],
});

Error handling

Two errors are specific to MCP flows:

Error code Description
resource_parameter_required isMcp is true but the request doesn't include a resource parameter.
misplaced_resource_parameter A resource was found both in the resource property and in extraQueryParameters. Use only one.

Both errors are thrown as ClientAuthError. For more information, see MSAL Node FAQs.

Samples

  • MCP Flows Sample — Express app demonstrating MCP with authorization code and silent flows.

Next steps

Initialize public client applications

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